Communication system and method where message length is assigned based on message preference

ABSTRACT

A method and communication system has been developed to increase the number of messages sent over a bandwidth limited channel and/or under noisy conditions by using a variable message length encoding and decoding scheme. With this technique, the messages having a higher probability of being sent are shorter as compared to the messages that are less likely to be sent under the current conditions. With this technique, a higher number of transactions per unit of time can be communicated and/or executed over a given bandwidth limited channel. When the transmitted message is received, the receiver does not know the message length, but the receiver deduces the length by using information from various error detection and correction techniques, such as forward error correction (FEC) and cyclic redundancy check (CRC) techniques.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/929,161, filed Nov. 14, 2019, which is hereby incorporated byreference. U.S. patent application Ser. No. 15/929,161, filed Nov. 14,2019, claims the benefit of U.S. Patent Application No. 62/767,211,filed Nov. 14, 2018, which are hereby incorporated by reference.

BACKGROUND

Typical over the air (OTA) radio transmissions can have significantlatencies when transmitted over long distances such as across oceans.Moreover, these transmission channels can be rather noisy which in turnincreases the need for error correction. This additional errorcorrection information typically increases the size of the message. Highfrequency (HF) radio communication channels of most long-distancecommunication systems are limited by the available assigned radiobandwidth and channel capacity at any given time. When using the HFradio channel in a financial high-frequency trading application,increasing the number of messages increases the profit potential of thesystem.

Thus, there is a need for improvement in this field.

SUMMARY

A unique method and communication system has been developed to increasethe number of messages sent over a bandwidth limited channel and/orunder noisy conditions by using a variable message length encoding anddecoding scheme in which the messages that have the higher probabilityof being sent are shorter as compared to the messages that are lesslikely to be sent under the current conditions. In other words, themessage length increases as the expected probability of the messagebeing sent is lower. By way of analogy, words in the English language(as well as other languages) that are commonly used, such as “a” and“the”, are typically shorter than words that are used less often like“Mississippi.” With this encoding scheme, the number of messages thatcan be sent on average over a particular channel can be increased.

This technique can be especially helpful in high latency conditionswhere the channels have limited bandwidth. Some non-limiting examplesinclude worldwide communications across or between continents,transoceanic communications, aircraft communications, and spacecraftcommunications. For instance, this technique can be helpful incontrolling remote spacecraft probes that have high latency and lowbandwidth communication conditions where communication timing iscritical. In other examples, this method can be used for communicatingwith submerged submarines, satellites, and remote surgical robots. Otheruse case examples include trading financial instruments. This techniqueand system can be used in other fields such as providing news and/orremotely controlling equipment.

Typical OTA radio transmissions can have significant latencies whentransmitted over long distances such as across oceans. Moreover, thesetransmission channels can be rather noisy which in turn increases theneed for error correction. This additional error correction informationtypically increases the size of the message. This unique method has beendeveloped to increase the number of messages sent over such radiochannels by using variable length messages where the types of messageshaving the higher probability of being transmitted are shorter thanthose with a lower probability of being used to make a trade or performsome other transaction. With this technique, a higher number oftransactions per unit of time can be communicated and/or executed over agiven bandwidth limited channel. When the transmitted message isreceived, the receiver does not know the message length, but thereceiver deduces the length by using information from various errordetection and correction techniques, such as forward error correction(FEC) and cyclic redundancy check (CRC) techniques.

It should be appreciated that the system and methods described hereinaddress several issues. For instance, by using a table of variablelength messages where the shortest messages are the most probable orcommon, a larger number of messages can be communicated over a limitedbandwidth channel over a period of time as compared to a set of constantlength messages that need to cover all possibilities. Support forvariable length messages at the baseband level allows mixing of messagelengths as will occur when the modems change operating modes which maybe done independently of the baseband processing portion of the system.It is practical to use the message code table definitions to includevariable levels of error control so that message security and accuracycan be adjusted according to message impact in case of false detectionor error. This extra protection may be included directly into thetranslation table or may be implemented by adding additional FECprotection in the modem. Compression of some messages into shortermessages also provides the possibility of increasing the error overhead,and thus, it provides more error protection for such messages.

The system and techniques as described and illustrated herein concern anumber of unique and inventive aspects. Some, but by no means all, ofthese unique aspects are summarized below.

Aspect 1 generally concerns a method that includes communicatingmessages having variable lengths over a communication channel.

Aspect 2 generally concerns the method of any previous aspect whichincludes creating a message code table that includes message groups withdifferent message lengths.

Aspect 3 generally concerns the method of any previous aspect whichincludes assigning higher preference messages to shorter message lengthgroups and lower preference messages to longer message length groups.

Aspect 4 generally concerns the method of any previous aspect in whichthe preference is based at least on probability that the message will besent.

Aspect 5 generally concerns the method of any previous aspect in whichthe preference is based at least on financial benefit of the message.

Aspect 6 generally concerns the method of any previous aspect whichincludes communicating the message code table to a receiver for themessages.

Aspect 7 generally concerns the method of any previous aspect whichincludes transmitting the message code table over a high latency, highbandwidth channel.

Aspect 8 generally concerns the method of any previous aspect in whichthe message code table is created in at least part by a computer at atransmitter.

Aspect 9 generally concerns the method of any previous aspect in whichthe message code table is created in at least part by a computer at areceiver.

Aspect 10 generally concerns the method of any previous aspect whichincludes selecting a financial trading strategy.

Aspect 11 generally concerns the method of any previous aspect whichincludes developing a set of possible trading commands based on thefinancial trading strategy.

Aspect 12 generally concerns the method of any previous aspect whichincludes estimating probabilities that the possible trading commandswill be issued.

Aspect 13 generally concerns the method of any previous aspect whichincludes assigning highest probability trading commands to a shortestmessage group.

Aspect 14 generally concerns the method of any previous aspect whichincludes assigning next priority commands to a next longer message groupthat has message lengths longer than the shortest message group.

Aspect 15 generally concerns the method of any previous aspect whichincludes transmitting the messages using a low latency, low bandwidthchannel.

Aspect 16 generally concerns the method of any previous aspect whichincludes communicating the messages using skywave propagation.

Aspect 17 generally concerns the method of any previous aspect in whichthe communication channel includes a primary channel.

Aspect 18 generally concerns the method of any previous aspect in whichthe primary channel includes a high frequency radio channel.

Aspect 19 generally concerns the method of any previous aspect in whichthe communication channel includes a backend channel.

Aspect 20 generally concerns the method of any previous aspect whichincludes encoding the messages with the variable lengths with at leastan error correction code.

Aspect 21 generally concerns the method of any previous aspect in whichthe messages with the variable lengths include at least forward errorcorrection (FEC).

Aspect 22 generally concerns the method of any previous aspect in whichthe messages with the variable lengths include at least a checksum.

Aspect 23 generally concerns the method of any previous aspect in whichthe messages with the variable lengths include at least a cyclicredundancy check (CRC).

Aspect 24 generally concerns the method of any previous aspect whichincludes appending a newly received symbol for one of the messages topreviously received symbols.

Aspect 25 generally concerns the method of any previous aspect whichincludes decoding one of the messages using forward error correction(FEC).

Aspect 26 generally concerns the method of any previous aspect in whichthe determining one of the messages is valid based on a validity of achecksum for the message.

Aspect 27 generally concerns the method of any previous aspect whichincludes decoding the messages using forward error correction (FEC) andcyclic error correction (CRC).

Aspect 28 generally concerns the method of any previous aspect whichincludes decoding the messages in a serial manner by cycling throughlarger message groups.

Aspect 29 generally concerns the method of any previous aspect whichincludes decoding the messages in a parallel manner by analyzing allpotential message group lengths simultaneously.

Aspect 30 generally concerns the method of any previous aspect whichincludes decoding the messages in which higher use probability messagesare encoded to have a shorter length as compared to lower useprobability messages.

Aspect 31 generally concerns the method of any previous aspect in whichthe messages concern one or more high-speed financial tradingtransactions.

Aspect 32 generally concerns the method of any previous aspect in whichthe message has a variable length.

Aspect 33 generally concerns the method of any previous aspect whichincludes decoding the messages without knowledge of length and timing ofthe message.

Aspect 34 generally concerns the method of any previous aspect whichincludes increasing error correction overhead for the messages.

Aspect 35 generally concerns the method of any previous aspect whichincludes providing higher degree of error protection by increasing errorcorrection overhead.

Aspect 36 generally concerns the method of any previous aspect whichincludes reducing false positive detection by increasing errorcorrection overhead.

Aspect 37 generally concerns the method of any previous aspect whichincludes encoding higher preference messages to shorter message lengthgroups and lower preference messages to longer message length groups.

Aspect 38 generally concerns a method of increasing the number ofpossible messages traversing a bandwidth-constrained radiocommunications system by creating message translation tables where aftertranslation higher probability messages output from the table have ashorter length than the lower probability messages.

Aspect 39 generally concerns the method of any previous aspect in whichthe messages contain data related to high-speed financial tradingtransactions.

Aspect 40 generally concerns the method of any previous aspect in whichthe error correction overhead is increased for messages requiring ahigher degree of protection from errors and/or false positive detection.

Aspect 41 generally concerns a method for the detection of variablelength messages without a-priori knowledge of the message length, nortiming.

Aspect 42 generally concerns the method of any previous aspect in whichthe messages contain data related to high-speed financial tradingtransactions.

Aspect 43 generally concerns the method of any previous aspect in whichthe error correction overhead is increased for messages requiring ahigher degree of protection from errors and/or false positive detection.

Aspect 44 generally concerns a system for performing the method of anyprevious aspect.

Further forms, objects, features, aspects, benefits, advantages, andembodiments of the present invention will become apparent from adetailed description and drawings provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a communication system according to oneexample.

FIG. 2 is a diagrammatic view of a communication system according toanother example.

FIG. 3 is a diagrammatic view of the FIG. 2 communication system beingused to communicate across an ocean.

FIG. 4 is a diagrammatic view of the FIG. 2 communication system thatshows further details.

FIG. 5 is a diagrammatic view of a communication system according to afurther example.

FIG. 6 is a flowchart illustrating a general method of encoding anddecoding one or more variable length messages.

FIG. 7 is a flowchart illustrating a method for developing a messagecode table.

FIG. 8 is a diagrammatic view of a first example of a message grouptable structure.

FIG. 9 is a diagrammatic view of a specific example for the FIG. 8message group table structure.

FIG. 10 is a diagrammatic view of a second example of a message grouptable structure.

FIG. 11 is a flowchart illustrating a method of decoding one or moremessages with variable lengths according to one example.

FIG. 12 is a diagram illustrating another method of decoding messageswith variable lengths.

FIG. 13 is a diagrammatic view of a decoder system according to anotherexample.

FIG. 14 is a diagram illustrating a technique in which the decoders inthe FIG. 13 decoder system use to decode messages with variable lengths.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates. One embodiment of the invention is shown in great detail,although it will be apparent to those skilled in the relevant art thatsome features that are not relevant to the present invention may not beshown for the sake of clarity.

The reference numerals in the following description have been organizedto aid the reader in quickly identifying the drawings where variouscomponents are first shown. In particular, the drawing in which anelement first appears is typically indicated by the left-most digit(s)in the corresponding reference number. For example, an elementidentified by a “100” series reference numeral will likely first appearin FIG. 1 , an element identified by a “200” series reference numeralwill likely first appear in FIG. 2 , and so on.

FIG. 1 shows a generic version of a communication system 100 accordingto one example. As shown, the communication system 100 includes aninformation source 105 and an information destination 110. Theinformation source 105 and information destination 110 operativelycommunicate with one another through one or more communication channels115. Communication over these communication channels 115 can be one-waytype communications and/or two-way type communications. In theillustrated example, the communication channels 115 between theinformation source 105 and information destination 110 include a primarycommunication channel 120 and a backend communication channel 125. Inother examples, the communication system 100 can include just a singlecommunication channel 115 or more than two communication channels 115.

As will be explained in further detail below, the communication system100 can be used in a number of situations, especially in situationswhere the information source 105 and information destination 110 arelocated physically remote from one another. The communication system 100for instance can be used for private, commercial, medical, military,and/or governmental purposes. For the purposes of explanation, thecommunication system 100 will be described for use with a financialtrading system, but it should be recognized that the communicationsystem 100 can be adapted for other uses such as for issuing militarycommands and performing remote telemedicine procedures. In this example,the information source 105 and information destination 110 generallyrepresent the locations of the computer systems for remotely locatedstock/commodity exchanges and/or financial institutions that trade onthose exchanges. Some examples of these exchanges include the New YorkStock Exchange (NYSE), the NASDAQ Stock Market, Tokyo Stock Exchange(TYO), the Shanghai Stock Exchange, the Hong Kong Stock Exchange,Euronext, London Stock Exchange, Shenzhen Stock Exchange, Toronto StockExchange, Bombay Stock Exchange, Chicago Mercantile Exchange (CME),Chicago Board of Trade (CBOT), and the New York Mercantile Exchange(NYMEX), just to name a few.

As shown in FIG. 1 , the information source 105 and informationdestination 110 are physically separated by a distance (“D”) 130. Forinstance, the exchanges represented by the information source 105 andinformation destination 110 can be separated by mountains, continents,and even oceans. This physical distance 130 creates a delay or latencyin communications between the information source 105 and informationdestination 110 locations. Normally, but not always, the greater thedistance 130, the longer the latency for a given communication channel115. In most cases, the distance 130 between these exchanges preventsdirect line of sight communications which further increases latency aswell as increases the risk for communication errors. For instance, theinformation destination 110 can be located past the radio horizon forthe information source 105. With trading as well as other activities,time and communication accuracy are crucial. Any delays can causetraders to lose money, and likewise, any communication errors can causea loss. Communication errors can be reduced but usually at the cost ofhigher latency and/or greater bandwidth requirements. Most communicationchannels 115 have limited bandwidth to some degree. The latency andbandwidth capabilities can vary depending on the construction and typeof communication channel 115.

As can be seen, the primary communication channel 120 has a primarychannel latency (“ΔT_(P)”) 135 and a primary channel bandwidth (“B_(P)”)140. The backend channel latency 145 primary communication channel 120has a backend channel latency (“ΔT_(B)”) 145 and a backend channelbandwidth (“B_(B)”) 150. The communication channels 115 in FIG. 1 canhave the same latency and bandwidth properties or different latencyand/or bandwidth as well as other properties. In one example, theprimary channel latency 135 of the primary communication channel 120 isless than the backend channel latency 145 of the backend communicationchannel 125, and the primary channel bandwidth 140 of the primarycommunication channel 120 is less than the backend channel bandwidth 150of the backend communication channel 125. In some variations of thisexample, the primary communication channel 120 is a wirelesscommunication channel (e.g., radio), and the backend communicationchannel 125 is a wired type communication channel (e.g., fiber opticcable). In one particular form, the primary communication channel 120uses a skywave communication technique, and the backend communicationchannel 125 includes a non-skywave path such as a fiber optic cable. Inother examples, the primary communication channel 120 and backendcommunication channel 125 represent different communication channels 115for the same type of communication mode. For instance, primarycommunication channel 120 and backend communication channel 125represent wireless communication channels having different frequencybands, and in one example, both communication channels 115 utilize highfrequency (HF) radio to communicate via skywave propagation. With theprimary communication channel 120 and backend communication channel 125having different frequencies, the primary communication channel 120 andbackend communication channel 125 can have different latencies,bandwidths, and/or communication error rates. For instance, the primarycommunication channel 120 in one situation can be noisier than thebackend communication channel 125, but the primary communication channel120 can have a shorter latency than the backend communication channel125.

The HF radio communication channel 115 of the communication system 100can be limited by the available assigned radio bandwidth and channelcapacity at any given time. When using the HF radio communicationchannel 115 in a financial high frequency trading application,increasing the number of messages increases the profit potential of thecommunication system 100. As will be further explained below, a uniquemethod has been developed to increase the number of messages sent over abandwidth-limited wireless communication channel 115 by using variablelength messages where the types of messages having the higherprobability of being transmitted are shorter than those with a lowerprobability of being used to make a trade or perform some othertransaction. With this technique, a higher number of transactions perunit of time can be communicated and/or executed. In the communicationsystem 100, the receiver or information destination 110 does not need toknow the message length, but the information destination 110 deduces thelength by using information from various error detection and correctiontechniques, such as forward error correction (FEC) and cyclic redundancycheck (CRC) techniques, with one or more decoder units. For practicalreasons, the messages in one particular variation are aligned to bemodulated symbol boundaries as determined by the modulation method usedand the overhead associated with the FEC and CRC checksum.

FIG. 2 illustrates a specific example of a communication system 200 ofthe FIG. 1 communication system 100 configured to transfer dataaccording to the unique technique described herein. Like in the FIG. 1communication system 100, the communication system 200 in FIG. 2includes the information source 105, information destination 110, andcommunication channels 115 that include the primary communicationchannel 120 and backend communication channel 125. Specifically, thecommunication system 200 in FIG. 2 is configured to transfer data via alow latency, low bandwidth communication link 204 and separate data viaa high latency, high bandwidth communication link 208. The low latency,low bandwidth communication link 204 and high latency, high bandwidthcommunication link 208 provide separate connections between a firstcommunication node 212 and a second communication node 216. The lowlatency, low bandwidth communication link 204 may be configured totransmit data using electromagnetic waves 224 passing through free spacevia skywave propagation between a transmitting antenna 228 and areceiving antenna 232. The electromagnetic waves 224 may be generated bya transmitter in the first communication node 212, passed along atransmission line 236 to the transmitting antenna 228. Theelectromagnetic waves 224 may be radiated by the transmitting antenna228 encountering an ionized portion of the atmosphere 220. This radiatedelectromagnetic energy may then be refracted by the ionized portion ofthe atmosphere 220 causing the electromagnetic waves 224 to redirecttoward the earth 256. The electromagnetic waves 224 may be received bythe receiving antenna 232 coupled to the second communication node 216by the transmission line 240. As illustrated in FIG. 2 , a transmittingcommunication node may use skywave propagation to transmitelectromagnetic energy long distances across the surface of the earth256 without the need of one or more transmission lines 236 to carry theelectromagnetic energy.

Data may also be transmitted between the first communication node 212and second communication node 216 using the high latency, high bandwidthcommunication link 208. As illustrated in FIG. 2 , the high latency,high bandwidth communication link 208 may be implemented using atransmission line 244 passing through the earth 256, which may includepassing under or through an ocean or other body of water. As shown inFIG. 2 , the high latency, high bandwidth communication link 208 mayinclude one or more repeaters 252. FIG. 2 illustrates four repeaters 252along the transmission line 244 although any suitable number ofrepeaters 252 may be used. The transmission line 244 may also have norepeaters 252 at all. Although FIG. 2 illustrates the low latency, lowbandwidth communication link 204 transmitting information from the firstcommunication node 212 to the second communication node 216, the datatransmitted may pass along the low latency, low bandwidth communicationlink 204 and high latency, high bandwidth communication link 208 in bothdirections.

As shown, the communication system 200 further includes a client 260that has a connection 264 to the first communication node 212. Theclient 260 is configured to send instructions over the connection 264 tothe first communication node 212. In the illustrated example, theconnection 264 includes a wireless connection 266 such as a microwavenetwork. At the first communication node 212, the instructions areprepared to be sent to the second communication node 216, either by thelow latency, low bandwidth communication link 204 or the high latency,high bandwidth communication link 208, or both. As shown, the secondcommunication node 216 is connected to an instruction processor 268 viaa connection 272. It should be recognized that the connection 272 caninclude wireless connection 266 like a microwave or other type ofwireless connection. The client 260 may be any business, group,individual, and/or entity that desires to send directions over adistance. The instruction processor 268 may be any business, group,individual, and/or entity that is meant to receive or act upon thoseinstructions. In some embodiments, the connection 264 and connection 272may be unnecessary as the client 260 may send the data to be transmitteddirectly from the first communication node 212 or the secondcommunication node 216 may be connected directly to the instructionprocessor 268. The communication system 200 may be used for any kind oflow-latency data transmission that is desired. As one example, theclient 260 may be a doctor or surgeon working remotely while theinstruction processor 268 may be a robotic instrument for working on apatient.

In some embodiments, the client 260 may be a financial instrument traderand the instruction processor 268 may be a stock exchange. The tradermay wish to provide instructions to the stock exchange to buy or sellcertain securities or bonds at specific times. Alternatively oradditionally, the instructions are in the form of news and/or otherinformation supplied by the trader and/or a third party organization,such as a news organization or a government. The trader may transmit theinstructions to the first communication node 212 which sends theinstructions and/or news to the second communication node 216 using thetransmitting antenna 228, receiving antenna 232, and/or by thetransmission line 244. The stock exchange can then process the actionsdesired by the trader upon receipt of the instructions and/or news.

The communication system 200 may be useful for high-frequency trading,where trading strategies are carried out on computers to execute tradesin fractions of a second. In high-frequency trading, a delay of meremilliseconds may cost a trader millions of dollars; therefore, the speedof transmission of trading instructions is as important as the accuracyof the data transmitted. In some embodiments, the trader may transmitpreset trading instructions or conditions for executing a trade to thesecond communication node 216, which is located within close proximityto a stock exchange, using the high latency, high bandwidthcommunication link 208 at a time before the trader wishes to execute atrade. These instructions or conditions may require the transmission ofa large amount of data, and may be delivered more accurately using thehigh latency, high bandwidth communication link 208. Also, if theinstructions or conditions are sent at a time prior to when a trade iswished to be executed, the higher latency of the high latency, highbandwidth communication link 208 can be tolerated.

The eventual execution of the instructions may be accomplished by thetrader transmitting triggering data to the communication system 200 onwhich the instructions are stored. Alternatively or additionally, thetriggering data can includes news and/or other information supplied bythe trader and/or a separate, third party organization. Upon receipt ofthe triggering data, the trading instructions are sent to the stockexchange and a trade is executed. The triggering data that istransmitted is generally a much smaller amount of data than theinstructions; therefore, the triggering data may be sent over the lowlatency, low bandwidth communication link 204. When the triggering datais received at the second communication node 216, the instructions for aspecific trade are sent to the stock exchange. Sending the triggeringdata over the low latency, low bandwidth communication link 204 ratherthan the high latency, high bandwidth communication link 208 allows thedesired trade to be executed as quickly as possible, giving the trader atime advantage over other parties trading the same financialinstruments.

The configuration shown in FIG. 2 is further illustrated in FIG. 3 wherethe first communication node 212 and the second communication node 216are geographically remote from one another separated by a substantialportion of the surface of the earth 256. This portion of the earth'ssurface may include one or more continents, oceans, mountain ranges,and/or other geographic areas. For example, the distance spanned in FIG.2 may cover a single continent, multiple continents, an ocean, and thelike. In one example, the first communication node 212 is in Chicago,Ill. in the United States of America, and the second communication node216 is in London, England, in the United Kingdom. In another example,the first communication node 212 is in New York City, N.Y., and thesecond communication node 216 is in Los Angeles, Calif., both citiesbeing in North America. As shown, the transmitting antenna 228 andreceiving antenna 232 are separated by a distance greater than the radiohorizon such that no line of sight communications can be made. Instead,a skywave communication technique is used in which the electromagneticwaves 224 of the low latency, low bandwidth communication link 204 areskipped multiple times between the transmitting antenna 228 andreceiving antenna 232. Any suitable combination of distance,communication nodes, and communications links is envisioned that canprovide satisfactory latency and bandwidth.

FIG. 2 illustrates that skywave propagation allows electromagneticenergy to traverse long distances. Using skywave propagation, the lowlatency, low bandwidth communication link 204 transmits theelectromagnetic waves 224 into a portion of the atmosphere 220 that issufficiently ionized to refract the electromagnetic waves 224 toward theearth 256. The waves may then be reflected by the surface of the earth256 and returned to the ionized portion of the upper atmosphere 220where they may be refracted toward earth 256 again. Thus electromagneticenergy may “skip” repeatedly allowing the low latency, low bandwidthsignals electromagnetic waves 224 to cover distances substantiallygreater than those which may be covered by non-skywave propagation.

FIG. 4 shows a specific implementation of the FIG. 2 communicationsystem 200. As can be seen, the first communication node 212 in FIG. 4includes a modulator 405, a radio transmitter 410, and a fiber optictransmitter 415. The modulator 405 includes one or more processors andmemory along with other electronics, software, and/or firmwareconfigured to modulate the message and/or other information using theabove-mentioned variable messaging length technique which will befurther described below. The radio transmitter 410 is operativelyconnected to the modulator 405 so as to transmit the message and/orother data to the second communication node 216 via the transmittingantenna 228 over one or more wireless communication channels 115. In thedepicted example, the radio transmitter 410 transmits the message and/orother data via the primary communication channel 120. The fiber optictransmitter 415 is operatively connected to the modulator 405 and afiber optic cable 420 that forms at least part of the backendcommunication channel 125. The fiber optic transmitter 415 is configuredto transmit to the second communication node 216 one or more messagetables and/or other information, such as a duplicate copy of the messagetransmitted by the radio transmitter 410, via the backend communicationchannel 125.

The second communication node 216 in FIG. 4 includes a demodulator 425,a radio receiver 430, and a fiber optic receiver 435. The demodulator425 includes one or more processors and memory along with otherelectronics, software, and/or firmware configured to demodulate themessage and/or other information from the first communication node 212using the above-mentioned technique which will be further describedbelow. The radio receiver 430 is operatively connected to thedemodulator 425 so as to receive the message and/or other data from thefirst communication node 212 via the receiving antenna 232. In theillustrated example, the radio receiver 430 again receives the messageand/or other data via the primary communication channel 120. The fiberoptic receiver 435 is operatively connected to the demodulator 425 andthe fiber optic cable 420. The fiber optic receiver 435 is configured toreceive from the fiber optic transmitter 415 of the first communicationnode 212 the message tables and/or other information, such as aduplicate copy of the message from the modulator 405.

It should be recognized that the communication system 200 in FIG. 4 canfacilitate one-way communication or two-way communication. For example,the modulator 405 can be configured to act as a modulator-demodulator(modem), and the demodulator 425 can likewise be a modem. The HF radiotransmitter 410 in certain variations can be configured to receivewireless communications so as to act as a wireless transceiver.Similarly, the HF radio receiver 430 can also be a wireless transceiver.Both the fiber optic transmitter 415 and fiber optic receiver 435 can befiber optic transceivers to facilitate two-way communication.

FIG. 5 shows another variation of the communication system 100 in FIG. 1that can perform the variable length messaging technique describedherein. As can be seen, a communication system 500 in FIG. 5 isconstructed in a similar fashion and shares a number of components incommon with the communication system 200 of FIGS. 2, 3, and 4 . Forinstance, the communication system 500 includes the modulator 405 andthe radio transmitter 410 with the transmitting antenna 228 of the typedescribed before. Moreover, the communication system 500 includes thedemodulator 425 and the radio receiver 430 with the receiving antenna232 of the kind mentioned above. As can be seen, however, the fiberoptic transmitter 415, fiber optic cable 420, and fiber optic receiver435 have been eliminated such that all communications are wireless, andmore particularly, through skywave communication. In one variation, thecommunication system 500 includes a single communication channel 115 inthe form of the low latency, low bandwidth communication link 204 thatforms the primary communication channel 120. In another variation, theradio communication between the radio transmitter 410 and radio receiver430 is through two or more HF communication channels 115 such that oneforms the primary communication channel 120 and the other forms thebackend communication channel 125. In one version, the primarycommunication channel 120 and the backend communication channel 125 canhave generally the same data bandwidth and/or latency, and in otherversions, the primary communication channel 120 and backendcommunication channel 125 can have different data bandwidths and/orlatencies. The modulator 405 in the illustrated example is connected tothe client 260 through a transmitter data network 505. The demodulator425 is connected to the instruction processor 268 through a receiverdata network 510. In one form, the transmitter data network 505 andreceiver data network 510 are high speed data networks.

The technique or method of using one or more variable length messages inthe systems described before as well as other systems will now begenerally described with reference to a flowchart 600 shown in FIG. 6 .For explanation purposes, the technique will be described with referenceto the communication system 200 shown in FIGS. 2, 3, and 4 , but itshould be recognized that this method can be used in other systems likethe FIG. 1 communication system 100 and/or the FIG. 5 communicationsystem 500. As noted before, this method is configured to increase thenumber of messages sent over a bandwidth limited communication channel115 by using a variable message length encoding and decoding scheme inwhich the messages that have the higher probability of being sent areshorter as compared to the messages that are less likely to be sentunder the current conditions. In other words, the message lengthincreases as the expected probability of the message being sent islower. By way of analogy, words in the English language (as well asother languages) that are commonly used, such as “a” and “the”, aretypically shorter than words that are used less often like“Mississippi.” With this encoding scheme, the number of messages thatcan be sent on average over a particular communication channel 115 canbe increased.

This technique can be especially helpful in high latency conditionswhere the communication channels 115 have limited bandwidth. Somenon-limiting examples include worldwide communications across or betweencontinents, transoceanic communications, aircraft communications, andspacecraft communications. For instance, this technique can be helpfulin controlling remote spacecraft probes that have high latency and lowbandwidth communication conditions where communication timing iscritical. In other examples, this method can be used for communicatingwith submerged submarines, satellites, and remote surgical robots. Toaid understanding, this technique will be described in reference totrading financial instruments, but it should be recognized that thistechnique can be used in other fields such as providing news and/orremotely controlling equipment.

Referring again to FIGS. 2, 3, and 4 , the low latency, low bandwidthcommunication link 204 of the communication system 200 can be limited bythe available assigned radio bandwidth and channel capacity at any giventime. When using the low latency, low bandwidth communication link 204in a financial high frequency trading application, increasing the numberof messages increases the profit potential of the communication system200. Again, this unique method has been developed to increase the numberof messages sent over a bandwidth-limited wireless communication channel115 by using variable length messages where the types of messages havingthe higher probability of being transmitted are shorter than those witha lower probability of being used to make a trade or perform some othertransaction. With this technique, a higher number of transactions perunit of time can be communicated and/or executed. In the communicationsystem 200, the demodulator 425 of the second communication node 216does not need to know the message length, but the demodulator 425deduces the length by using information from various error detection andcorrection techniques, such as forward error correction (FEC) and cyclicredundancy check (CRC) techniques, with one or more decoder units. Forpractical reasons, the messages in one particular variation are alignedto be modulated symbol boundaries as determined by the modulation methodused and the overhead associated with the FEC and CRC checksum.

Looking at FIG. 6 , the modulator 405 in stage 605 in one exampledevelops a message code table (or codebook) in which the messages forthe most common financial transactions for a particular trading strategyhave a shorter length and the messages for financial transactions thatare less common have a higher length. For example, if the tradingstrategy is to short sell a specific blue-chip stock, then the messagesor instructions related to selling the blue-chip stock will be shorterthan other messages like those for buying stocks in other companies. Inpractice, these trading strategies can become quite complex.Alternatively or additionally, this message frequency or probability canbe augmented based on other factors. For example, the message may beshorter when the financial benefit of the transaction is significantlyhigher than a more common message. While a command may be more commonlyused, the financial benefit of the command may be relatively small ascompared to a less commonly used command that provides a significantlyhigher return. In one alternative example, the message length solelydepends on the overall expected return for a given command eitherindividually or in the aggregate. Those messages with higher returns aremade typically smaller than those with lower financial benefits. In afurther example, a combination approach is used in which a number offactors are used to determine the message length including, but notlimited to, message commonality, financial rewards for the message,and/or message impact on other parties or overall strategy.

In one form, the processor, memory, and software inside the modulator405 are used to develop this message code table, but it should berecognized that the message code table can be developed in other ways.For instance, the modulator 405 can be hardwired and/or have firmwarethat develops this message code table. In other examples, one or moreseparate computers alone or in conjunction with the modulator 405develop the message code table. In still yet further examples, variousinputs, such as news, stock information, and human inputs, are used tohelp develop these message code tables. While the term “table” is usedto describe the message code table, the message code table can beorganized in a variety of data structure forms and should not be limitedto just data tables such as those found in relational databases. It ispractical to use the message code table definitions to include variablelevels of error control so that message security and accuracy can beadjusted according to message impact in case of false detection orerror. This extra protection may be included directly into thetranslation table or may be implemented by adding additional FECprotection in the modem.

Once the message code table is developed, the modulator 405 thenpublishes the message code table by sending the message code table tothe second communication node 216 and/or other reception locations. Themessage code table can be sent in any number of ways. For example, themessage code table can be transmitted via one or more of thecommunication channels 115 and/or physically transported such as via anelectronic storage media (e.g., DVD, flash drive, etc.). In one example,the message code table is just transmitted over the backendcommunication channel 125, such as the fiber optic cable 420 in FIG. 4 ,to preserve bandwidth on the primary communication channel 120, and inanother example, the message code table is just transmitted on theprimary communication channel 120 like the low latency, low bandwidthcommunication link 204 in FIGS. 4 and 5 . In still yet furthervariations, a combination approach is used in which all or part of themessage code table is transmitted in both the primary communicationchannel 120 and backend communication channel 125 so as to addredundancy and reduce errors. For instance, the radio transmitter 410via the transmitting antenna 228 in FIG. 4 transmits all or part of themessage code table over the low latency, low bandwidth communicationlink 204 to the receiving antenna 232 of the radio receiver 430 at thedemodulator 425, and the fiber optic transmitter 415 at the firstcommunication node 212 transmits all or part of the message code tablevia the fiber optic cable 420 of the high latency, high bandwidthcommunication link 208 to the fiber optic receiver 435 of the secondcommunication node 216. Once the message code table arrives at thesecond communication node 216, the processor of the demodulator 425stores the message code table locally in memory inside the demodulator425 and/or remotely such as in a remote server (e.g., for backup orother purposes). To offload work and free up operational bandwidth atthe second communication node 216, the message code table can bereceived and, if needed, preprocessed at a receiver located relativelyclose to the second communication node 216. From this closer receiverstation, the message code table can be sent to the demodulator 425 ofthe second communication node 216 via a high speed network like viamicrowave transmission.

The modulator 405 of the first communication node 212 can develop and/orpublish these message code tables one time, periodically, or on anas-needed basis. A combination of approaches can be used. For instance,the modulator 405 can develop and publish on a periodic basis, say oncean hour or every business day, but the modulator 405 can develop andsend a full or partially updated message table when certain marketconditions occur that warrant changing the trading strategy which inturn changes message probabilities or prevalence. The firstcommunication node 212 then can send partial or full updates of themessage table to the second communication node 216 and/or other nodes.

Referring again to the flowchart 600 in FIG. 6 , when a particularcommand, such as for a particular trade or trading strategy, needs to beissued, the modulator 405 encodes the command or message using thecipher of the message coding table in stage 610. For instance, aspecific market condition and/or a piece of news may necessitate thesale of one or more stocks. A stockbroker or, more likely, a computerfor the stockbroker issues the stock trade command and/or retransmissionof the particular news piece to the first communication node 212. Basedon the current message code table, the modulator 405 encodes all or partof the message or command. The message can be encoded using any numberof FEC techniques, and the encoded message normally includes some typeof checksum. In one version, the message is encoded using a combinationof a Tail-Biting Viterbi FEC and a CRC checksum. Other FEC codes andchecksums may be used in other variations. The radio transmitter 410 viathe transmitting antenna 228 transmits all or part of the encodedmessage over the low latency, low bandwidth communication link 204 viaskywave propagation in stage 610. The first communication node 212 viathe fiber optic transmitter 415 may also transmit all or part of theencoded message over the fiber optic cable 420 of the high latency, highbandwidth communication link 208. With the communication system 500 inFIG. 5 , the encoded message is only sent over the low latency, lowbandwidth communication link 204 via a HF radio transmission using askywave communication technique.

In stage 615, the radio receiver 430 via the receiving antenna 232receives the encoded message from the first communication node 212, andthe radio receiver 430 of the second communication node 216 sends theencoded message to the demodulator 425. Typically, but not always, theradio receiver 430 sends individual symbols of the encoded message tothe demodulator 425 as the symbols are received so as to speed up thedecoding process. In some cases, the radio receiver 430 can buffer thesymbols when the symbol count for a new message is below the smallestmessage size for a given message code table. However, in most cases, thereceived signal is directly sent from the radio receiver 430 to thedemodulator 425 for processing.

As will be explained in greater detail below, the demodulator 425 usesthe previously received message table in stage 615 to decode themessage. The demodulator 425 does not know the length of the transmittedmessage. In other words, the demodulator 425 does not know when themessage will end, because the demodulator 425 does not know the size ofthe message frame for the message. As each symbol is received, thedemodulator 425 converts the signal to digital data and buffers thesymbol with other symbols in memory that were received after the lastdetermined message to form a pseudo-message that is tested. The messageframe of the shortest supported rate from the message code table is usedby the demodulator 425 to determine if this collection of receivedsymbols or pseudo-message is a valid message. For example, thedemodulator 425 performs a checksum or other error detecting techniqueto determine if the collection of symbols forms a valid message. Symbolscontinue to be added to the buffer and the checksum test is performedagain on this larger frame of symbols. The demodulator 425 can performthis checking in a serial fashion and/or through a parallel processingtechnique. The demodulator 425 for example can include more than onephysical and/or software-based demodulator to facilitate parallelprocessing. Each of the physical or virtual demodulators 425 can beassigned a specific message length to determine message validity byperforming the checksum and/or other error detection functions at thesame time.

Once the demodulator 425 detects a valid message in stage 615, such asby calculating a valid checksum, the demodulator 425 sends the decodedmessage or command to perform an action or not in stage 620. Forexample, the message can be sent to the instruction processor 268 inFIG. 2 . In stage 620, a trade of a specific stock for instance can beautomatically executed by computers upon receipt of this commandmessage. It should be also recognized that no actual action may occur instage 620. For example, the message may provide news or otherinformation that is later used as part of the overall trading strategy,or the message may indicate to hold onto a particular financialinstrument and to not sell the instrument.

One technique for developing and publishing the message code table ofstage 605 will now be described with reference to a flowchart 700 inFIG. 7 . The actions of this technique will be described as beingperformed via the processor, memory, and software of the modulator 405in FIGS. 4 and 5 , but it should be recognized that this technique canall or in part be performed by other equipment and/or other entities.For instance, some or all of these acts can be performed by a clientstockbroker computer that transmits all or part of the message codetable to the modulator 405 and/or demodulator 425. In another example,the demodulator 425 creates and publishes the table. Again, while thistechnique will be described with reference to financial transactions, itshould be recognized that this technique can be used in other fields.

As shown in FIG. 7 , the client, such as a stock trader, in stage 705manually and/or automatically selects a specific trading strategydepending a wide variety factors, including market conditions, economicconditions, and the news, to name just a few. Based on the selectedtrading strategy, the client, a computer system for the client, and/orthe modulator 405 develops a list of possible trading commands in stage710. These commands can include, but are not limited to, buying,selling, trading, and/or keeping financial instruments at differentprice levels. This set of potential trading commands can in part bebased on past trading strategies.

The variable length message code table is based on the trading strategyto be implemented. Some strategies may have a smaller possible messageset than others. Each message is given a message use probability basedon past frequency of execution of identical or similar tradingstrategies. Commands or messages with a higher probability of being sentare given shorter message lengths than lower probability messages. Inlight of historical and/or other data, the client, the computer systemfor the client, and/or the modulator 405 in stage 715 assigns commandprobabilities or frequency categories to each command based on thelikelihood the specific command will be issued under the designatedtrading strategy. Once more, these estimated probabilities can beaugmented or replaced by other factors. For instance, the probabilitythat a message will be sent can be factored by the financial benefit ofthe command such that the command is graded or ranked based on theoverall expected net value or financial benefit under the designatedtrading strategy.

In the following manner, a message code table is then built with eachmessage describing a specific type of action or command. In stage 720,the client, a computer system for the client, and/or the modulator 405assigns the most frequently sent and/or highest financially rankedmessage to the shortest message group (i.e., message size with thelowest length). Within each message size group, a unique message code isassigned to each command or action.

To provide a very simplified example, the shortest message group may betwo-bits long such that four (4) commands can be assigned to the two-bitmessage group. In this example, the four most common commands for thedesignated trading strategy is “buy one share of company X”, “sell twoshares of company Y”, “hold the shares of company Y”, and “buy threeshares of company Z”. For this shortest, two-bit message group, the “buyone share of company X” command is assigned a message signifier of zero(i.e., 00 in binary), the “sell two shares of company Y” is designatedby a message with the number one (i.e., Olin binary) as its contents,the “hold the shares of company Y” is designated by the number two(i.e., 10 in binary), and the “buy three shares of company Z” isdesignated by the number three (i.e., 11 in binary). The order of thesecommands within the particular message group length can be in noparticular order, ordered based on probability, or based on some otherscheme. When for instance the demodulator 425 (FIGS. 4 and 5 ) decodes amessage to have the value of “3” (i.e., 11 in binary), a trade will beexecuted in which three shares of company Z are bought.

In one particular embodiment, message lengths are integer number ofbytes with the last bit of the byte ending in a fixed value, such aszero (0), and with another value, such as one (1), indicating anextension of the message following the current message. Other messageextension approaches can be used in other examples. For instance,messages can be built in blocks of multiple bytes using an extensionindicator. In another embodiment, a message header bit indicates themessage length by having the number of leading zeros (0's) or ones (1's)indicating the expected message length. The message code tabledefinitions can also include variable levels of error control so thatmessage security and accuracy can be adjusted according to messageimpact in case of false detection or error. This extra protection may beincluded directly into the translation table and/or may be implementedby adding additional FEC protection in the modem.

Once all of the spaces for the commands at the shortest message lengthare filled, the next remaining groups of commands with the next lowestprobability and/or rank are assigned in stage 725 to the next availableshortest group that has a message length longer than the first orhighest probability message group. Returning to the previous simplifiedtwo-bit message group length example, once all four numbers areassociated with commands in the two-bit message group length, the nexthighest probability level or ranked commands are then assigned to alonger, three-bit message group length. The modulator 405 (or clientsystem) checks to see if all of the commands have been assigned in stage730 and keeps on assigning messages to progressively longer messagegroups based on probability and/or rank in stage 725.

Once all of the commands have been assigned in stage 730, the modulator405 publishes the resulting message code table in stage 735 in the samemanner as described before by transmitting the message code table to thedemodulator 425 of the second communication node 216. Again, themodulator 405 can transmit the message code table via one or more of thecommunication channels 115 such as via the primary communication channel120 and/or backend communication channel 125. In one example, themodulator 405 transmits the message code table via the fiber optic cable420 that forms the high latency, high bandwidth communication link 208.The message code table in one variation is published to both the radiotransmission and reception equipment. In one embodiment, the fiber opticcable 420 is used, but any available communication channel 115 may beused. It should be noted that the fiber optic channel is likely to havemore propagation delay than the main wireless channel used to send thetrading commands. Once the message code table is set at both modulator405 and demodulator 425, the trading strategy is then executed using thevariable length message code table. When it is time to change strategiesor conditions change, a new command to message mapping may beconstructed and published in the same fashion as described above (e.g.,starting again at stage 705).

In another example, the demodulator 425 or a computer at the secondcommunication node 216 performs the acts of creating and publishing themessage code table in accordance with the flowchart 700 in FIG. 7 . Inthis example, the demodulator 425 can maintain in memory informationconcerning the message frequency probabilities and other data (e.g.,financial conditions, weather conditions, noise conditions, etc.) frommultiple different transmitters and/or other sources. With this example,the demodulator 425 is able to create the message code table based on alarger data set which presumably would increase the quality of themessage code table. Once the message code table is completed, thedemodulator 425 in stage 735 transmits the message code table to themodulator 405 of the first communication node 212 such as through thelow latency, low bandwidth communication link 204 and/or high latency,high bandwidth communication link 208.

There are a large number of techniques that can be used to set themessage lengths for the message groups in the message code tables. FIG.8 shows a first example of a message group table structure 800. In theFIG. 8 message group table structure 800, the message groups grow orexpand in a linear fashion. Specifically, the message group tablestructure 800 shows a linear expansion where each message size grows byM-bits. In this case, the most common messages will be represented by acode word of length M. FIG. 9 shows an example message group tablestructure 900 of the FIG. 8 message group table structure 800 in whichthe message length is incremented by 8 bits. As shown in FIG. 9 , if Mis 8 bits, there are 256 messages available from the first messageprobability group (i.e., Group 1). Thus, 256 commands or messages havingthe greatest expected use frequency (or other rank) can be sent with amessage length of 8 bits. Messages having lower use probability can beassigned to the second message probability group (i.e., Group 2) orsubsequent groups. In the second message group, 65,536 messages of16-bit length can be sent. Generally, two messages from the firstprobability message group, which have the highest expectation of beingsent, can be sent in the same time as a single message from the secondmessage probability group. It therefore should be recognized that onaverage more messages for a given time period can be transmitted usingthis variable length message communication technique as compared tofixed message length communication techniques. FIG. 10 shows anotherexample of a message group table structure 1000 in which a geometricprogression is used for increasing message sizes for the messageprobability groups.

In one form, the above-discussed message size coding techniques assumeeach variable length OTA message has its own CRC and FEC protection. Inother variations, this method is extended to include multiplevariable-length messages in CRC/FEC protected OTA packets. For thisvariation, each message includes an indication of the message length.For instance, a message assigned to the first message probability grouphas a single leading zero (0) for group 1, a message assigned to thesecond group has two leading zeros (00), and so on.

During transmission of the messages, the message length can vary fromone message to the next depending on which message is sent and to whichmessage probability group it belongs. Returning to the FIG. 9 example, afirst message belonging to message probability group 4 would have alength of 32-bits, and the next or second message belonging to messageprobability group 1 would be 8 bits long. Subsequent messages could havethe same or different message lengths depending on the message. At theradio receiver 430, the demodulator 425 does not know ahead of time thelength of the message the radio receiver 430 is receiving. Since themessage length is not known ahead of time, a unique technique or methodhas been developed that allows the demodulator 425 to detect messagevalidity and length concurrently. In one version, this technique uses acombination of a Tail-Biting Viterbi FEC and a CRC checksum. Other FECcodes and checksums may be used in other variations. Radio and othertransmissions tend to be noisy, and as such, there is a significant riskof errors in the received message. False positives or false negativescan occur during the transmission and decoding process. Both of theseerrors can be problematic, especially when dealing with financialinstrument transactions. For example, false positives occur when amessage is considered valid when in fact the message is not valid (i.e.,not a message at all). As should be recognized, this false positivemessage can cause a financial transaction to occur when the transactionwas not desired. This decoding approach is designed to prevent falsepositives (i.e., messages declared valid are not actually due to noiseor bit errors).

One technique for receiving and decoding the transmitted variable lengthmessages of stage 615 in FIG. 6 will now be described with reference toa flowchart 1100 shown in FIG. 11 . The technique will be described withreference to the communication system 200 in FIG. 4 and thecommunication system 500 in FIG. 5 , but it should be recognized thatother communication systems 100 can utilize this method. The demodulator425 and radio receiver 430 have one or more processors, memory,software, and other electronics that are configured to perform thismethod. While this method will be described as being performed by thedemodulator 425 and radio receiver 430, it should be appreciated thatall or parts of these acts can be performed by other systems.

Looking at FIGS. 4, 5, and 11 , the demodulator 425 in stage 1105 waitsfor a new symbol to arrive at the radio receiver 430. When a new symbolfrom the low latency, low bandwidth communication link 204 is detectedby the radio receiver 430, the symbol is buffered in the memory of thedemodulator 425 along with the previously received symbols. The newlyreceived symbol will normally add one or more bits to the receivedqueue. This series of the symbols received by the radio receiver 430 andstored in memory can include all or part of the message. However, thesesymbols can also include fill data (i.e., blank spaces between messages)and/or noise. The demodulator 425 analyzes all of these symbolsregardless of their content (e.g., fill data, noise, etc.) to determinewhether a message has been received. In other words, the demodulator 425must consider every symbol, whether actually containing message data,fill data, or noise as a potential packet start. Due to the variablelength of the messages, however, the demodulator 425 does not know thelength of the message.

In stage 1110, the demodulator 425 initially selects the frame ormessage length from the message probability group having the shortestlength. Normally, but not always, the demodulator 425 starts with theshortest length supported by the message code table. Using the messagegroup table structure 900 in FIG. 9 as an example, the demodulator 425picks the 8 bit message length, which is the shortest, from the firstmessage probability group (i.e., Group 1). With message frame or lengthselected, the demodulator 425 in stage 1115 decodes via FEC thepseudo-message formed by the buffer of symbols in memory using thecurrent message length as a basis. Returning to the previous example,the demodulator 425 performs FEC decoding using an 8-bit frame length.In one embodiment, this algorithm is a Tail-Biting Viterbi Algorithm.However, other FEC decoding algorithms can be used. For example, FECdecoding can be a different tail-biting convolutional decoding algorithmor a block code such as Reed Solomon.

In stage 1120, the demodulator 425 calculates a cyclic redundancy check(CRC) and/or other checksum for the FEC decoded data, and the resultingchecksum information for the message is checked by the demodulator 425in stage 1120 to see if it matches the expected checksum. Forexplanation purposes, the technique will be described as using a CRC,but it should be recognized other types of checksums can be used.Typically, but not always, the expected CRC or checksum value ispackaged or contained within the transmitted message, and the FECdecoded data includes the expected checksum value. In other variations,the expected checksum value can be transmitted or otherwise providedseparately. For example, the message code table provided to thedemodulator 425 can already include the expected checksum value for eachmessage. The demodulator 425 performs a CRC on the FEC decoded data onorder to calculate the checksum. If the checksum does not match theexpected checksum in stage 1120, the demodulator 425 in stage 1125determines whether the next largest message size is supported by themessage code table. Normally, the demodulator 425 increments to thelarger length of the next message probability group. So, returning tothe previous FIG. 9 example, the demodulator 425 would increment up fromthe 8-bit length of Group 1 to the 16-bit length of Group 2 which issupported by the message group table structure 900.

When the next length is supported in stage 1125, the demodulator 425cycles back to stage 1110 and selects this next larger message lengthwhich in this example is 16-bits. The demodulator 425 in stage 1115performs FEC decoding using this now larger 16-bit frame. This largerframe includes the most recent symbol as well as the ones immediatelybefore so as to add up to the 16-bit length. In other words, thedemodulator 425 works back in time by tacking together the recent symbolwith the more recently received ones to add up to the current frame size(i.e., 16 bits in this case) for decoding purposes. After decoding thenext length in stage 1115, the demodulator 425 in stage 1120 determinesif the checksum is valid. If the checksum is not valid, the demodulator425 in stage 1125 determines if the next message length is validaccording to the scheme used for the message code table. If the next,larger length is valid, the demodulator 425 cycles again to stage 1110to perform the same decoding and checks for the larger sized message instage 1110, stage 1115, and stage 1120.

On the other hand, when the message length is not supported, thedemodulator 425 cycles back to stage 1105 so as to wait for the nextsymbol to be received. Looking at the message group table structure 900in the FIG. 9 example, a next message size larger than 40 bits (i.e.,after Group 5) is considered not supported in stage 1125. In otherwords, the demodulator 425 knows the modulator 405 would not encode amessage size larger than specified by the shared message code table.When this occurs in stage 1125, the demodulator 425 starts again instage 1105 and waits for the next symbol arrival. In stage 1110, thedemodulator 425 starts again with the smallest message (e.g., 8 bits inFIG. 9 ), and the process cycle continues.

Once the CRC or other checksum from the FEC decoding stage 1115 matchesin stage 1120, the demodulator 425 declares the message valid andprepares a data packet to transmit the message or command in stage 1130to the instruction processor 268. For instance, if a checksum match isfound, then a data packet is declared and sent out the receiver userdata port. The sent message for instance can be packaged fortransmission over high speed data networks. Again, this message can beused to execute (or not) a financial transaction.

FIG. 12 shows a diagram 1200 that provides more details for thetechnique illustrated by the flowchart 1100 in FIG. 11 . The demodulator425 in stage 1205 waits for the next symbol in the same fashion as stage1105 in FIG. 11 . In stage 1210, the newly received symbol is appendedto the older symbols stored in the memory of the demodulator 425. Thedemodulator 425 in stage 1215 converts these received symbols in thememory buffer to digital data so as to facilitate later decoding. Likein stage 1110 in FIG. 11 , the demodulator 425 in stage 1110 initiallyselects the smallest message length in stage 1220 and progressivelyworks to decoding and checking larger message sizes. In this example,the initial message length starts from a zero-bit length or position. Asin stage 1115, the demodulator 425 in stage 1225 runs an FEC algorithmto decode the message and remove any FEC overhead such as extraneousparity check bits. Like stage 1120 before in FIG. 11 , the demodulator425 in stage 1230 in the diagram 1200 of FIG. 12 performs a CRC check tosee if the message is valid. If not, the demodulator 425 checks to seeif the next message length is supported in stage 1235 (1125 in FIG. 11). When supported, the demodulator 425 cycles back to stage 1220 andperforms FEC decoding and CRC checking in stage 1225 and stage 1230 forthe now larger message length. The demodulator 425 continues to cyclethrough larger message lengths until the last message length for themessage code table is exceeded in stage 1235 or the CRC check issatisfied. When the message size limit is reached, the demodulator 425proceeds to wait for the next symbol, and the cycle continues again. Onthe other hand, when a valid message is detected in stage 1230, thedemodulator 425 strips any CRC bits from the message in stage 1240. Thenow stripped message is repackaged with packet overhead and user data isadded to the packet in stage 1245 and stage 1250, respectively. The newmessage can then be used to execute an action (620 in FIG. 6 ) such as afinancial transaction.

In the previous examples, the demodulator 425 performed the algorithm ina serial fashion by incrementing from the shortest to longest acceptablemessage lengths. In another variation, a parallel approach can be used.Considering that the HF radio symbol time is slow compared to the clocktime of modern signal processing and computer technology, a time-slicedapproach can be used to reduce the time for decoding and forwarding areceived message.

One example of a distance 130 that can be used in the demodulator 425for performing this parallel or time-sliced approach is depicted in FIG.13 . It should be recognized that the components of the decoder system1300 can be configured through hardware, software, and/or a combinedapproach. For example, these components can be virtual in that thecomponents exist as separate processes or algorithms in a computer orthe demodulator 425. In another example, the components can be in theform of dedicated hardware such as electronics specifically designed toperform at least a part of the decoding process. In one variation, thedecoder system 1300 is amenable to a field-programmable gate array(FPGA) and/or software implementation.

As shown, the decoder system 1300 includes an unframed demodulator dataoutput 1305, a plurality of decoders 1310, and a priority decoder 1315.The unframed demodulator data output 1305 provides the unframeddemodulator data to the decoders 1310. Once more, this unframed data mayor may not contain a message with an unknown length. The unframed datacontains a series of the symbols received by the radio receiver 430 andstored in memory. These symbols can include all or part of the message.However, these symbols can also include fill data (i.e., blank spacesbetween messages) and/or noise. The decoder system 1300 analyzes all ofthese symbols regardless of their content (e.g., fill data, noise, etc.)to determine whether a message has been received. In other words, thedecoder system 1300 must consider every symbol, whether actuallycontaining message data, fill data, or noise, as a potential packetstart. Due to the variable length of the messages, however, the decodersystem 1300 does not know the length of the message.

The decoders 1310 receive the unframed message data from the unframeddemodulator data output 1305. Each of the decoders 1310 is dedicated toa specific message length associated with a message probability group.In other words, the system has a series of decoders 1310 each dedicatedto decode a specific message length. In the illustrated example, thedecoder system 1300 has a set of M decoders 1310. For instance, thedepicted decoders 1310 include a shortest length decoder 1320, anintermediate length decoder 1325, and a longest length decoder 1330along with other decoders 1310. The shortest length decoder 1320 isconfigured to decode and detect if a message having the shortest messagelength (e.g., from group 1) has been received. The longest lengthdecoder 1330 is configured to decode and detect if a message having thelongest message length according to the message code table has beenreceived. The intermediate length decoder 1325 is designed to decode anddetect a message with a length between the longest and shortest lengths.Using FIG. 9 as an example, the shortest length decoder 1320 wouldanalyze using 8 bit message lengths (group 1), the intermediate lengthdecoder 1325 would analyze using 16 bit message lengths (group 2), andthe longest length decoder 1330 would analyze using 40 bit messagelengths (group 5). In one form, the decoders 1310 decode and detectmessages in a similar fashion as described before by using FEC decodingof the message and checking for a valid CRC or checksum. In certainembodiments, this is done by using a combination of a Tail-BitingViterbi FEC and a CRC checksum. Other FEC codes and checksums can beused in other examples.

With each decoder 1310 being dedicated to a specific message, thedifferent message lengths can be analyzed in parallel if needed so as tospeed up the overall decoding and message detection process. Theseparallel decoders 1310 may run concurrently or may be run in sequence ifthe processing at the receiver is sufficient to execute all functions inOTA symbol time.

Once one of the decoders 1310 detects a valid message (e.g., the messagehas a valid checksum), the decoder 1310 sends a data or message detectsignal to the priority decoder 1315 along with the decoded data ormessage. The data detect signal can be in the form of a binary signal(i.e., yes or no) indicating that the message was detected or anon-binary/analog form providing additional information. For instance,when in a non-binary form, the data detect signal can indicate aconfidence level that the message is valid. The priority decoder 1315 isconfigured to accept the data from the first decoder 1310 to declaredata found overriding the others. The priority decoder 1315 is furtherconfigured to inform the decoders 1310 that a valid message has beendetected so that the decoders 1310 are then able to search for the nextvalid message. For example, when the intermediate length decoder 1325detects a valid message, the intermediate length decoder 1325 sends adata detect signal to the priority decoder 1315 along with the decodedmessage or data. The priority decoder 1315 then alerts all or some ofthe decoders 1310 about the detection, and in response, the decoders1310 decode the next data from the unframed demodulator data output1305. In case of ties between the decoders 1310, the priority decoder1315 can use any number of tie breaking rules such as the smallermessage length message wins.

The decoded message and data detect signal are then sent to the clientor other destination in a similar fashion as described before. Throughthe data detect signal signifying decoding confidence, the client mayfind the information useful in deciding whether a particular action iswarranted. For example, the data detect signal may only marginallyindicate that the message is valid. In such a case, the client may takean approach of disregarding such marginal messages.

FIG. 14 shows a diagram 1400 that depicts a process each of the decoders1310 in FIG. 13 perform to decode and detect valid messages. It shouldbe appreciated that the process is similar to the process illustrated bythe diagram 1200 in FIG. 12 , but the process has been stripped down byeliminating the cycling through each message length because each of thedecoders 1310 is dedicated to a specific message length.

The decoder 1310 in stage 1405 waits for the next symbol in the samefashion as described before. In stage 1405, the newly received symbol isappended to the older symbols stored in the memory of the decoder 1310.The decoder 1310 in stage 1410 converts these received symbols in thememory buffer to digital data so as to facilitate later decoding. Thedecoder 1310 in stage 1415 runs an FEC algorithm to decode the messageand remove any FEC overhead such as extraneous parity check bits. Inthis case, the FEC is done based on the specified message length for thedecoder 1310. The decoder 1310 in stage 1420 performs a CRC check to seeif the message is valid. In one form, a combination Tail-Biting ViterbiFEC and a CRC checksum is used. Other FEC codes and checksums may beused. If the CRC is not valid in stage 1420, the decoder 1310 proceedsto wait for the next symbol in stage 1405, and the cycle continuesagain. On the other hand, when a valid message is detected in stage1420, the decoder 1310 strips any CRC bits from the message in stage1425. The now stripped message is repackaged with packet overhead anduser data is added to the packet in stage 1430. The decoder 1310 sends adata detect signal and the decoded message to the priority decoder 1315.This new message can then be used to execute an action (620 in FIG. 6 )such as a financial transaction.

It should be appreciated that the system and methods described hereinaddress several issues. For instance, by using a table of variablelength messages where the shortest messages are the most probable orcommon, a larger number of messages can be communicated over a limitedbandwidth channel over a period of time as compared to a set of constantlength messages that need to cover all possibilities. Support forvariable length messages at the baseband level allows mixing of messagelengths as will occur when the modems change operating modes which maybe done independently of the baseband processing portion of the system.It is practical to use the message code table definitions to includevariable levels of error control so that message security and accuracycan be adjusted according to message impact in case of false detectionor error. This extra protection may be included directly into thetranslation table or may be implemented by adding additional FECprotection in the modem. Compression of some messages into shortermessages also provides the possibility of increasing the error overhead,and thus, it provides more error protection for such messages.

Glossary of Terms

The language used in the claims and specification is to only have itsplain and ordinary meaning, except as explicitly defined below. Thewords in these definitions are to only have their plain and ordinarymeaning. Such plain and ordinary meaning is inclusive of all consistentdictionary definitions from the most recently published Webster'sdictionaries and Random House dictionaries. As used in the specificationand claims, the following definitions apply to these terms and commonvariations thereof identified below.

“Antenna” or “Antenna system” generally refers to an electrical device,or series of devices, in any suitable configuration, that convertselectric power into electromagnetic radiation. Such radiation may beeither vertically, horizontally, or circularly polarized at anyfrequency along the electromagnetic spectrum. Antennas transmitting withcircular polarity may have either right-handed or left-handedpolarization. In the case of radio waves, an antenna may transmit atfrequencies ranging along an electromagnetic spectrum from extremely lowfrequency (ELF) to extremely high frequency (EHF). An antenna or antennasystem designed to transmit radio waves may comprise an arrangement ofmetallic conductors (elements), electrically connected (often through atransmission line) to a receiver or transmitter. An oscillating currentof electrons forced through the antenna by a transmitter can create anoscillating magnetic field around the antenna elements, while the chargeof the electrons also creates an oscillating electric field along theelements. These time-varying fields radiate away from the antenna intospace as a moving transverse electromagnetic field wave. Conversely,during reception, the oscillating electric and magnetic fields of anincoming electromagnetic wave exert force on the electrons in theantenna elements, causing them to move back and forth, creatingoscillating currents in the antenna. These currents can then be detectedby receivers and processed to retrieve digital or analog signals ordata. Antennas can be designed to transmit and receive radio wavessubstantially equally in all horizontal directions (omnidirectionalantennas), or preferentially in a particular direction (directional orhigh gain antennas). In the latter case, an antenna may also includeadditional elements or surfaces which may or may not have any physicalelectrical connection to the transmitter or receiver. For example,parasitic elements, parabolic reflectors or horns, and other suchnon-energized elements serve to direct the radio waves into a beam orother desired radiation pattern. Thus antennas may be configured toexhibit increased or decreased directionality or “gain” by the placementof these various surfaces or elements. High gain antennas can beconfigured to direct a substantially large portion of the radiatedelectromagnetic energy in a given direction that may be vertical,horizontal, or any combination thereof. Antennas may also be configuredto radiate electromagnetic energy within a specific range of verticalangles (i.e. “takeoff angles) relative to the earth in order to focuselectromagnetic energy toward an upper layer of the atmosphere such asthe ionosphere. By directing electromagnetic energy toward the upperatmosphere at a specific angle, specific skip distances may be achievedat particular times of day by transmitting electromagnetic energy atparticular frequencies. Other examples of antennas include emitters andsensors that convert electrical energy into pulses of electromagneticenergy in the visible or invisible light portion of the electromagneticspectrum. Examples include light emitting diodes, lasers, and the likethat are configured to generate electromagnetic energy at frequenciesranging along the electromagnetic spectrum from far infrared to extremeultraviolet.

“Backend Communication Channel”, “Secondary Communication Channel”, or“Secondary Channel” generally refers to a communication pathway that isa main choice for transferring information. Typically, but not always,the secondary channel has one or more properties, such as latency orbandwidth, that make the channel less desirable over a primary channel.For example, a secondary channel can have a lower data rate and/orlatency as compared to a primary channel. A primary channel may supportthe transfer of information in one direction only, either directionalternately, or both directions simultaneously. The secondary channelcan for example include wired and wireless forms of communication.

“Band” or “Frequency Bandwidth” generally refer to a contiguous range offrequencies defined by an upper and lower frequency. Frequency bandwidthis thus typically expressed as a number of hertz (cycles per second)representing the difference between the upper frequency and the lowerfrequency of the band and may or may not include the upper and lowerfrequencies themselves. A “band” can therefore be defined by a givenfrequency bandwidth for a given region and designated with generallyagreed on terms. For example, the “20 meter band” in the United Statesis assigned the frequency range from 14 MHz to 14.35 MHz thus defining afrequency bandwidth of 0.35 MHz or 350 KHz. In another example, theInternational Telecommunication Union (ITU) has designated the frequencyrange from 300 Mhz to 3 GHz as the “UHF band”.

“Checksum” generally refers to data derived from a block of digital datafor the purpose of detecting errors that may have been introduced duringits transmission and/or storage. Typically, the checksum data isrelatively small-sized. By themselves, checksums are often used toverify data integrity, but checksums are not typically relied upon toverify data authenticity. The procedure or process that generates thechecksum from a data input is called a checksum function or checksumalgorithm. Depending on the use case, a good checksum algorithm willusually output a significantly different value, even for small changesmade to the data input. When the computed checksum for a data inputmatches the stored value of a previously computed checksum, theprobability that the data has not been accidentally altered and/orcorrupted is high. Some checksum algorithm techniques include paritybyte, sum complement, and position-dependent algorithms. Check digitsand parity bits are special cases of checksums that are usuallyappropriate for small blocks of data. Some error-correcting codes arebased on special checksums which not only detect common errors, but theerror correcting code in some cases further helps in the recovery of theoriginal data.

“Command” or “Command Data” generally refers to one or more directives,instructions, algorithms, or rules controlling a machine to take one ormore actions, alone or in combination. A command may be stored,transferred, transmitted, or otherwise processed in any suitable manner.For example, a command may be stored in a memory or transmitted over acommunication network as electromagnetic radiation at any suitablefrequency passing through any suitable medium.

“Communication Link” generally refers to a connection between two ormore communicating entities and may or may not include a communicationschannel between the communicating entities. The communication betweenthe communicating entities may occur by any suitable means. For examplethe connection may be implemented as an actual physical link, anelectrical link, an electromagnetic link, a logical link, or any othersuitable linkage facilitating communication. In the case of an actualphysical link, communication may occur by multiple components in thecommunication link configured to respond to one another by physicalmovement of one element in relation to another. In the case of anelectrical link, the communication link may be composed of multipleelectrical conductors electrically connected to form the communicationlink. In the case of an electromagnetic link, elements of the connectionmay be implemented by sending or receiving electromagnetic energy at anysuitable frequency, thus allowing communications to pass aselectromagnetic waves. These electromagnetic waves may or may not passthrough a physical medium such as an optical fiber, or through freespace, or any combination thereof. Electromagnetic waves may be passedat any suitable frequency including any frequency in the electromagneticspectrum. In the case of a logical link, the communication links may bea conceptual linkage between the sender and recipient such as atransmission station in the receiving station. Logical link may includeany combination of physical, electrical, electromagnetic, or other typesof communication links.

“Communication Node” generally refers to a physical or logicalconnection point, redistribution point or endpoint along a communicationlink. A physical network node is generally referred to as an activeelectronic device attached or coupled to a communication link, eitherphysically, logically, or electromagnetically. A physical node iscapable of sending, receiving, or forwarding information over acommunication link. A communication node may or may not include acomputer, processor, transmitter, receiver, repeater, and/ortransmission lines, or any combination thereof.

“Computer” generally refers to any computing device configured tocompute a result from any number of input values or variables. Acomputer may include a processor for performing calculations to processinput or output. A computer may include a memory for storing values tobe processed by the processor, or for storing the results of previousprocessing. A computer may also be configured to accept input and outputfrom a wide array of input and output devices for receiving or sendingvalues. Such devices include other computers, keyboards, mice, visualdisplays, printers, industrial equipment, and systems or machinery ofall types and sizes. For example, a computer can control a network ornetwork interface to perform various network communications uponrequest. The network interface may be part of the computer, orcharacterized as separate and remote from the computer. A computer maybe a single, physical, computing device such as a desktop computer, alaptop computer, or may be composed of multiple devices of the same typesuch as a group of servers operating as one device in a networkedcluster, or a heterogeneous combination of different computing devicesoperating as one computer and linked together by a communicationnetwork. The communication network connected to the computer may also beconnected to a wider network such as the Internet. Thus a computer mayinclude one or more physical processors or other computing devices orcircuitry, and may also include any suitable type of memory. A computermay also be a virtual computing platform having an unknown orfluctuating number of physical processors and memories or memorydevices. A computer may thus be physically located in one geographicallocation or physically spread across several widely scattered locationswith multiple processors linked together by a communication network tooperate as a single computer. The concept of “computer” and “processor”within a computer or computing device also encompasses any suchprocessor or computing device serving to make calculations orcomparisons as part of the disclosed system. Processing operationsrelated to threshold comparisons, rules comparisons, calculations, andthe like occurring in a computer may occur, for example, on separateservers, the same server with separate processors, or on a virtualcomputing environment having an unknown number of physical processors asdescribed above. A computer may be optionally coupled to one or morevisual displays and/or may include an integrated visual display.Likewise, displays may be of the same type, or a heterogeneouscombination of different visual devices. A computer may also include oneor more operator input devices such as a keyboard, mouse, touch screen,laser or infrared pointing device, or gyroscopic pointing device to namejust a few representative examples. Also, besides a display, one or moreother output devices may be included such as a printer, plotter,industrial manufacturing machine, 3D printer, and the like. As such,various display, input and output device arrangements are possible.Multiple computers or computing devices may be configured to communicatewith one another or with other devices over wired or wirelesscommunication links to form a network. Network communications may passthrough various computers operating as network appliances such asswitches, routers, firewalls or other network devices or interfacesbefore passing over other larger computer networks such as the Internet.Communications can also be passed over the network as wireless datatransmissions carried over electromagnetic waves through transmissionlines or free space. Such communications include using Wi-Fi or otherWireless Local Area Network (WLAN) or a cellular transmitter/receiver totransfer data.

“Critical angle” generally refers to the highest angle with respect to avertical line extending to the center of the Earth at which anelectromagnetic wave at a specific frequency can be returned to theearth using skywave propagation.

“Critical Frequency” generally refers to the highest frequency that willbe returned to the Earth when transmitted vertically under givenionospheric conditions using skywave propagation.

“Cyclic Redundancy Check” or “CRC” generally refers to anerror-detecting code or technique to detect errors in digital data. Forexample, CRC is commonly used in digital networks and/or storage devicesto detect accidental changes to raw data. CRC is based on binarydivision, and CRC is also sometimes referred to as polynomial codechecksum. With CRC, blocks of data get encoded with or attached a shortcheck value that is based on the remainder of a polynomial division ofthe contents of the blocks of data. During retrieval or decoding, thecalculation is repeated. When the check values do not match, correctiveaction can be taken against data corruption. CRCs can be further used tofacilitate error correction. The check or data verification value is aredundancy because it expands the message without adding information.CRCs can be simple to implement in binary hardware, easy to analyzemathematically, and are good at detecting common errors caused by noisytransmission channels. Given the check value has a fixed length, thefunction that generates the check value is sometimes used as a hashfunction.

“Data Bandwidth” generally refers to the maximum throughput of a logicalor physical communication path in a communication system. Data bandwidthis a transfer rate that can be expressed in units of data transferredper second. In a digital communications network, the units of datatransferred are bits and the maximum throughput of a digitalcommunications network is therefore generally expressed in “bits persecond” or “bit/s.” By extension, the terms “kilobit/s” or “Kbit/s”,“Megabit/s” or “Mbit/s”, and “Gigabit/s” or “Gbit/s” can also be used toexpress the data bandwidth of a given digital communications network.Data networks may be rated according to their data bandwidth performancecharacteristics according to specific metrics such as “peak bit rate”,“mean bit rate”, “maximum sustained bit rate”, “information rate”, or“physical layer useful bit rate.” For example, bandwidth tests measurethe maximum throughput of a computer network. The reason for this usageis that according to Hartley's Law, the maximum data rate of a physicalcommunication link is proportional to its frequency bandwidth in hertz.Data bandwidth may also be characterized according to the maximumtransfer rate for a particular communications network. For example:

-   -   “Low Data Bandwidth” generally refers to a communications        network with a maximum data transfer rate that is less than or        about equal to 1,000,000 units of data per second. For example,        in a digital communications network, the unit of data is a bit.        Therefore low data bandwidth digital communications networks are        networks with a maximum transfer rate that is less than or about        equal to 1,000,000 bits per second (1 Mbits/s).    -   “High Data Bandwidth” generally refers to a communications        network with a maximum data transfer rate that is greater than        about 1,000,000 units of data per second. For example, a digital        communications network with a high data bandwidth is a digital        communications network with a maximum transfer rate that is        greater than about 1,000,000 bits per second (1 Mbits/s).

“Demodulation” generally refers to a process of extracting an originalinformation-bearing signal from a carrier wave.

“Demodulator” or “Detector” generally refers to a device, such as anelectronic circuit and/or computer, that extracts original informationfrom a received modulated waveform based on one or more properties ofthe waveform. For example, these properties of the waveform can includeamplitude, frequency, phase, and harmonics as well as other properties.After reception of the modulated carrier, the demodulator recovers theoriginal modulating signal by the process of demodulation or detection.One or more modulators can be integrated with one or more demodulatorsto form a modulator-demodulator (modem). As such, the term demodulatormay further refer to one or more parts, components, and/or software thatdemodulate within a modem.

“Electromagnet Radiation” generally refers to energy radiated byelectromagnetic waves. Electromagnetic radiation is produced from othertypes of energy, and is converted to other types when it is destroyed.Electromagnetic radiation carries this energy as it travels moving awayfrom its source at the speed of light (in a vacuum). Electromagneticradiation also carries both momentum and angular momentum. Theseproperties may all be imparted to matter with which the electromagneticradiation interacts as it moves outwardly away from its source.Electromagnetic radiation changes speed as it passes from one medium toanother. When transitioning from one media to the next, the physicalproperties of the new medium can cause some or all of the radiatedenergy to be reflected while the remaining energy passes into the newmedium. This occurs at every junction between media that electromagneticradiation encounters as it travels. The photon is the quantum of theelectromagnetic interaction and is the basic constituent of all forms ofelectromagnetic radiation. The quantum nature of light becomes moreapparent at high frequencies as electromagnetic radiation behaves morelike particles and less like waves as its frequency increases.

“Electromagnetic Spectrum” generally refers to the range of all possiblefrequencies of electromagnetic radiation.

“Electromagnetic Waves” generally refers to waves having a separateelectrical and a magnetic component. The electrical and magneticcomponents of an electromagnetic wave oscillate in phase and are alwaysseparated by a 90 degree angle. Electromagnetic waves can radiate from asource to create electromagnetic radiation capable of passing through amedium or through a vacuum. Electromagnetic waves include wavesoscillating at any frequency in the electromagnetic spectrum including,but not limited to, radio waves, visible and invisible light, X-rays,and gamma-rays.

“Error Correction Code”, “Error Correcting Code”, or “ECC” generallyrefers to data and/or algorithms for expressing a sequence of numbers orother data such that any errors which are introduced can be detected andcorrected within certain limitations based on the remaining numbers ordata. ECC is typically used for controlling errors in data overunreliable and/or noisy communication channels. For instance, the senderencodes the message with a redundant in the form of an ECC. There aretwo main categories of ECCs, block codes and convolution codes. Somenon-limiting examples of ECC codes include AN, BCH, Berger,constant-weight, convolutional, cyclic redundancy check (CRC), expander,group, Golay, Goppa, Hadamard, Hagelbarger, Hamming code, Latin squarebased, lexicographic, long, low-density parity-check (i.e., Gallagercode), LT, polar, raptor, Reed-Solomon error correction, Reed-Muller,repeat-accumulate, repetition (e.g., triple modular redundancy), spinal,rateless, nonlinear, tornado, near-optimal erasure correcting, turbocode, and Walsh-Hadamard codes.

“Fiber-optic Communication” generally refers to a method of transmittingdata from one place to another by sending pulses of electromagneticenergy through an optical fiber. The transmitted energy may form anelectromagnetic carrier wave that can be modulated to carry data.Fiber-optic communication lines that use optical fiber cables totransmit data can be configured to have a high data bandwidth. Forexample, fiber-optic communication lines may have a high data bandwidthof up to about 15 Tbit/s, about 25 Tbit/s, about 100 Tbit/s, about 1Pbit/s or more. Opto-electronic repeaters may be used along afiber-optic communication line to convert the electromagnetic energyfrom one segment of fiber-optic cable into an electrical signal. Therepeater can retransmit the electrical signal as electromagnetic energyalong another segment of fiber-optic cable at a higher signal strengththan it was received.

“Financial Instrument” generally refers to a tradable asset of any kind.General examples include, but are not limited to, cash, evidence of anownership interest in an entity, or a contractual right to receive ordeliver cash or another financial instrument. Specific examples includebonds, bills (e.g. commercial paper and treasury bills), stock, loans,deposits, certificates of deposit, bond futures or options on bondfutures, short-term interest rate futures, stock options, equityfutures, currency futures, interest rate swaps, interest rate caps andfloors, interest rate options, forward rate agreements, stock options,foreign-exchange options, foreign-exchange swaps, currency swaps, or anysort of derivative.

“Forward Error Correction” or FEC generally refers to a technique usedfor controlling errors in data transmission over unreliable or noisycommunication channels. Typically, but not always, a sender encodes themessage in a redundant way by using an error-correction code (ECC). Thisredundancy allows a receiver to detect a limited number of errors thatmay occur anywhere in the message, and the redundancy often allows theseerrors to be corrected without retransmission. FEC gives the receiverthe ability to correct errors without needing a reverse channel torequest retransmission of data. However, higher forward channelbandwidth is typically required. FEC can be used in situations whereretransmissions are costly or impossible, such as one-way communicationlinks and when transmitting to multiple receivers in multicast. FEC iscommonly used in modems. FEC information can also be added to massstorage devices to enable recovery of corrupted data. There aregenerally two types of FEC code categories, block codes and convolutioncodes. FEC block codes work on fixed-size blocks (or packets) of bits orsymbols of predetermined size. Some non-limiting examples of block codesinclude Reed-Solomon, Golay, BCH, multidimensional parity, and Hammingcodes. Typical block codes are usually decoded using hard-decisionalgorithms in which for every input and output signal a hard decision ismade whether it corresponds to a one or a zero bit. Convolutional FECcodes work on bit or symbol streams of arbitrary length. Convolutionalcodes are typically decoded using soft-decision algorithms like theViterbi, MAP or BCJR algorithms that process (discretized) analogsignals, and which allow for much higher error-correction performancethan hard-decision decoding. Convolutional FEC codes are most often softdecoded with the Viterbi algorithm, though other algorithms can be used.Viterbi decoding allows asymptotically optimal decoding efficiency withincreasing constraint length of the convolutional code, but at theexpense of exponentially increasing complexity. A convolutional codethat is terminated is also a block code in that it encodes a block ofinput data, but the block size of a convolutional code is generallyarbitrary, while block codes have a fixed size dictated by theiralgebraic characteristics. Types of termination for convolutional codesinclude tail-biting and bit-flushing. Some other non-limiting examplesof FEC techniques include turbo coding, low density parity check (LDPC),interleaving, and local decoding. Many FEC coders (but not all) can alsogenerate a bit-error rate (BER) signal which can be used as feedback tofine-tune the analog receiving electronics.

“Ground” is used more in an electrical/electromagnetic sense andgenerally refers to the Earth's surface including land and bodies ofwater, such as oceans, lakes, and rivers.

“Ground-wave Propagation” generally refers to a transmission method inwhich one or more electromagnetic waves are conducted via the boundaryof the ground and atmosphere to travel along the ground. Theelectromagnetic wave propagates by interacting with the semi-conductivesurface of the earth. In essence, the wave clings to the surfaces so asto follow the curvature of the earth. Typically, but not always, theelectromagnetic wave is in the form of a ground or surface wave formedby low-frequency radio waves.

“Identifier” generally refers to a name that identifies (that is, labelsthe identity of) either a unique thing or a unique class of things,where the “object” or class may be an idea, physical object (or classthereof), or physical substance (or class thereof). The abbreviation“ID” often refers to identity, identification (the process ofidentifying), or an identifier (that is, an instance of identification).An identifier may or may not include words, numbers, letters, symbols,shapes, colors, sounds, or any combination of those. The words, numbers,letters, or symbols may follow an encoding system (wherein letters,digits, words, or symbols represent ideas or longer identifiers) or theymay simply be arbitrary. When an identifier follows an encoding system,it is often referred to as a code or ID code. Identifiers that do notfollow any encoding scheme are often said to be arbitrary IDs becausethey are arbitrarily assigned without meaning in any other contextbeyond identifying something.

“Intersymbol Interference” or “ISI” generally refers to a form ofdistortion of a signal in which one symbol interferes with subsequentsymbols. Typically, but not always, ISI is an unwanted phenomenon as theprevious symbols have a similar effect as noise which make communicationless reliable. For example, the spreading of a pulse beyond the allottedtime interval causes the pulse to interfere with neighboring pulses. ISIis usually, but not always, caused by multipath propagation and/or theinherent linear or non-linear frequency response of a communicationchannel causing successive symbols to blur together.

“Ionosphere” generally refers to the layer of the Earth's atmospherethat contains a high concentration of ions and free electrons and isable to reflect radio waves. The ionosphere includes the thermosphere aswell as parts of the mesosphere and exosphere. The ionosphere extendsfrom about 25 to about 600 miles (about 40 to 1,000 km) above theearth's surface. The ionosphere includes a number of layers that undergoconsiderable variations in altitude, density, and thickness, dependingupon a number of factors including solar activity, such as sunspots.

“Jitter” generally refers to a variable delay in the receipt of atransmitted message. For example, jitter arises as messages arrive at aninput at varying intervals, and as a result, the receiver of the messagehas to wait a variable time before a data slot is available for messagetransport.

“Latency” generally refers to the time interval between a cause and aneffect in a system. Latency is physically a consequence of the limitedvelocity with which any physical interaction can propagate throughout asystem. Latency is physically a consequence of the limited velocity withwhich any physical interaction can propagate. The speed at which aneffect can propagate through a system is always lower than or equal tothe speed of light. Therefore every physical system that includes somedistance between the cause and the effect will experience some kind oflatency. For example, in a communication link or communications network,latency generally refers to the minimum time it takes for data to passfrom one point to another. Latency with respect to communicationsnetworks may also be characterized as the time it takes energy to movefrom one point along the network to another. With respect to delayscaused by the propagation of electromagnetic energy following aparticular propagation path, latency can be categorized as follows:

-   -   “Low Latency” generally refers to a period of time that is less        than or about equal to a propagation time that is 10% greater        than the time required for light to travel a given propagation        path in a vacuum. Expressed as a formula, low latency is defined        as follows:

${latency}_{low} \leq {\frac{d}{c} \cdot k}$

-   -   where:        -   d=distance (miles)        -   c=the speed of light in a vacuum (186,000 miles/sec)        -   k=a scalar constant of 1.1    -   For example, light can travel 25,000 miles through a vacuum in        about 0.1344 seconds. A “low latency” communication link        carrying data over this 25,000 mile propagation path would        therefore be capable of passing at least some portion of the        data over the link in about 0.14784 seconds or less.    -   “High Latency” generally refers to a period of time that is over        10% greater than the time required for light to travel a given        propagation path in a vacuum. Expressed as a formula, high        latency is defined as follows:

${latency}_{high} > {\frac{d}{c} \cdot k}$

-   -   where:        -   d=distance (miles)        -   c=the speed of light in a vacuum (186,000 miles/sec)        -   k=a scalar constant of 1.1    -   For example, light can travel 8,000 miles through a vacuum in        about 0.04301 seconds. A “high latency” communication link        carrying data over this transmission path would therefore be        capable of passing at least some portion of the data over the        link in about 0.04731 seconds or more.    -   The “high” and “low” latency of a network may be independent of        the data bandwidth. Some “high” latency networks may have a high        transfer rate that is higher than a “low” latency network, but        this may not always be the case. Some “low” latency networks may        have a data bandwidth that exceeds the bandwidth of a “high”        latency network.

“Maximum Usable Frequency (MUF)” generally refers to the highestfrequency that is returned to the earth using skywave propagation.

“Memory” generally refers to any storage system or device configured toretain data or information. Each memory may include one or more types ofsolid-state electronic memory, magnetic memory, or optical memory, justto name a few. By way of non-limiting example, each memory may includesolid-state electronic Random Access Memory (RAM), SequentiallyAccessible Memory (SAM) (such as the First-In, First-Out (FIFO) varietyor the Last-In-First-Out (LIFO) variety), Programmable Read Only Memory(PROM), Electronically Programmable Read Only Memory (EPROM), orElectrically Erasable Programmable Read Only Memory (EEPROM); an opticaldisc memory (such as a DVD or CD ROM); a magnetically encoded hard disc,floppy disc, tape, or cartridge media; or a combination of any of thesememory types. Also, each memory may be volatile, nonvolatile, or ahybrid combination of volatile and nonvolatile varieties.

“Message” generally refers to a discrete unit of communication intendedby a source for consumption by a recipient or group of recipients.

“Modem” or “Modulator-Demodulator” generally refers to a device, such asan electronic circuit and/or computer, that performs the functions ofmodulation and demodulation of a signal such as through a modulator anda demodulator.

“Modulation” generally refers to the process of varying one or moreproperties of a periodic waveform, called the carrier signal, with amodulating signal that typically contains information to be transmitted.

“Modulator” generally refers to a device, such as an electronic circuitand/or computer, that varies one or more properties of a periodicwaveform, called the carrier signal, with a modulating signal thattypically contains information to be transmitted. For example, theseproperties of the waveform can include amplitude, frequency, phase, andharmonics as well as other properties. By way of a non-limiting example,the modulator can control the parameters of a high-frequencyelectromagnetic information carrier in accordance with electricalsignals of the transmitted message. One or more modulators can beintegrated with one or more demodulators to form a modulator-demodulator(modem). As such, the term modulator may further refer to one or moreparts, components, and/or software that functions as a modulator withina modem.

“Network” or “Computer Network” generally refers to a telecommunicationsnetwork that allows computers to exchange data. Computers can pass datato each other along data connections by transforming data into acollection of datagrams or packets. The connections between computersand the network may be established using either cables, optical fibers,or via electromagnetic transmissions such as for wireless networkdevices. Computers coupled to a network may be referred to as “nodes” oras “hosts” and may originate, broadcast, route, or accept data from thenetwork. Nodes can include any computing device such as personalcomputers, phones, and servers as well as specialized computers thatoperate to maintain the flow of data across the network, referred to as“network devices”. Two nodes can be considered “networked together” whenone device is able to exchange information with another device, whetheror not they have a direct connection to each other. A network may haveany suitable network topology defining the number and use of the networkconnections. The network topology may be of any suitable form and mayinclude point-to-point, bus, star, ring, mesh, or tree. A network may bean overlay network which is virtual and is configured as one or morelayers that use or “lay on top of” other networks.

“Non-skywave propagation” generally refers to all forms of transmission,wired and/or wireless, in which the information is not transmitted byreflecting an electromagnetic wave from the ionosphere.

“Optical Fiber” generally refers to an electromagnetic waveguide havingan elongate conduit that includes a substantially transparent mediumthrough which electromagnetic energy travels as it traverses the longaxis of the conduit. Electromagnetic radiation may be maintained withinthe conduit by total internal reflection of the electromagneticradiation as it traverses the conduit. Total internal reflection isgenerally achieved using optical fibers that include a substantiallytransparent core surrounded by a second substantially transparentcladding material with a lower index of refraction than the core.Optical fibers are generally constructed of dielectric material that isnot electrically conductive but is substantially transparent. Suchmaterials may or may not include any combination of extruded glass suchas silica, fluoride glass, phosphate glass, Chalcogenide glass, orpolymeric material such as various types of plastic, or other suitablematerial and may be configured with any suitable cross-sectional shape,length, or dimension. Examples of electromagnetic energy that may besuccessfully passed through optical fibers include electromagnetic wavesin the near-infrared, mid-infrared, and visible light portion of theelectromagnetic spectrum, although electromagnetic energy of anysuitable frequency may be used.

“Optimum Working Frequency” generally refers to the frequency thatprovides the most consistent communication path via skywave propagation.It can vary over time depending on number of factors, such asionospheric conditions and time of day. For transmissions using the F2layer of the ionosphere the working frequency is generally around 85% ofthe MUF, and for the E layer, the optimum working frequency willgenerally be near the MUF.

“Packet Error Rate” or “Packet Error Ratio” or “PER” generally refers tothe number of incorrectly received data packets divided by the totalnumber of received packets in a digital transmission. Generally, apacket is declared incorrect if at least one bit is erroneous.

“Polarization” generally refers to the orientation of the electric field(“E-plane”) of a radiated electromagnetic energy wave with respect tothe Earth's surface and is determined by the physical structure andorientation of the radiating antenna. Polarization can be consideredseparately from an antenna's directionality. Thus, a simple straightwire antenna may have one polarization when mounted substantiallyvertically, and a different polarization when mounted substantiallyhorizontally. As a transverse wave, the magnetic field of a radio waveis at right angles to that of the electric field, but by convention,talk of an antenna's “polarization” is understood to refer to thedirection of the electric field. Reflections generally affectpolarization. For radio waves, one important reflector is the ionospherewhich can change the wave's polarization. Thus for signals received viareflection by the ionosphere (a skywave), a consistent polarizationcannot be expected. For line-of-sight communications or ground wavepropagation, horizontally or vertically polarized transmissionsgenerally remain in about the same polarization state at the receivinglocation. Matching the receiving antenna's polarization to that of thetransmitter may be especially important in ground wave or line-of-sightpropagation but may be less important in skywave propagation. Anantenna's linear polarization is generally along the direction (asviewed from the receiving location) of the antenna's currents when sucha direction can be defined. For instance, a vertical whip antenna orWi-Fi antenna vertically oriented will transmit and receive in thevertical polarization. Antennas with horizontal elements, such as mostrooftop TV antennas, are generally horizontally polarized (becausebroadcast TV usually uses horizontal polarization). Even when theantenna system has a vertical orientation, such as an array ofhorizontal dipole antennas, the polarization is in the horizontaldirection corresponding to the current flow. Polarization is the sum ofthe E-plane orientations over time projected onto an imaginary planeperpendicular to the direction of motion of the radio wave. In the mostgeneral case, polarization is elliptical, meaning that the polarizationof the radio waves varies over time. Two special cases are linearpolarization (the ellipse collapses into a line) as discussed above, andcircular polarization (in which the two axes of the ellipse are equal).In linear polarization the electric field of the radio wave oscillatesback and forth along one direction; this can be affected by the mountingof the antenna but usually the desired direction is either horizontal orvertical polarization. In circular polarization, the electric field (andmagnetic field) of the radio wave rotates at the radio frequencycircularly around the axis of propagation.

“Primary Communication Channel” or “Primary Channel” generally refers toa communication pathway that is a first choice for transferringinformation. Typically, but not always, the primary communicationchannel has one or more properties, such as latency or bandwidth, thatis desirable over others. For example, a primary communication channelcan have the highest data rate of all the channels sharing a commoninterface. A primary communication channel may support the transfer ofinformation in one direction only, either direction alternately, or bothdirections simultaneously. The primary communication channel can forexample include wired and wireless forms of communication.

“Processor” generally refers to one or more electronic componentsconfigured to operate as a single unit configured or programmed toprocess input to generate an output. Alternatively, when of amulti-component form, a processor may have one or more componentslocated remotely relative to the others. One or more components of eachprocessor may be of the electronic variety defining digital circuitry,analog circuitry, or both. In one example, each processor is of aconventional, integrated circuit microprocessor arrangement. A processoralso includes an Application-Specific Integrated Circuit (ASIC). An ASICis an Integrated Circuit (IC) customized to perform a specific series oflogical operations in controlling a computer to perform specific tasksor functions. An ASIC is an example of a processor for a special purposecomputer, rather than a processor configured for general-purpose use. Anapplication-specific integrated circuit generally is not reprogrammableto perform other functions and may be programmed once when it ismanufactured. In another example, a processor may be of the “fieldprogrammable” type. Such processors may be programmed multiple times “inthe field” to perform various specialized or general functions afterthey are manufactured. A field-programmable processor may include aField-Programmable Gate Array (FPGA) in an integrated circuit in theprocessor. FPGA may be programmed to perform a specific series ofinstructions which may be retained in nonvolatile memory cells in theFPGA. The FPGA may be configured by a customer or a designer using ahardware description language (HDL). An FPGA may be reprogrammed usinganother computer to reconfigure the FPGA to implement a new set ofcommands or operating instructions. Such an operation may be executed inany suitable means such as by a firmware upgrade to the processorcircuitry. Just as the concept of a computer is not limited to a singlephysical device in a single location, so also the concept of a“processor” is not limited to a single physical logic circuit or packageof circuits but includes one or more such circuits or circuit packagespossibly contained within or across multiple computers in numerousphysical locations. In a virtual computing environment, an unknownnumber of physical processors may be actively processing data, and theunknown number may automatically change over time as well. The conceptof a “processor” includes a device configured or programmed to makethreshold comparisons, rules comparisons, calculations, or performlogical operations applying a rule to data yielding a logical result(e.g. “true” or “false”). Processing activities may occur in multiplesingle processors on separate servers, on multiple processors in asingle server with separate processors, or on multiple processorsphysically remote from one another in separate computing devices.

“Radio” generally refers to electromagnetic radiation in the frequenciesthat occupy the range from 3 kHz to 300 GHz.

“Radio Horizon” generally refers to the locus of points at which directrays from an antenna are tangential to the ground. The radio horizon canbe approximated by the following equation:

d≃√{square root over (2h _(t))}+√{square root over (2h _(r))}

-   -   where:    -   d=radio horizon (miles)    -   h_(t)=transmitting antenna height (feet)    -   h_(r)=receiving antenna height (feet).

“Receive” generally refers to accepting something transferred,communicated, conveyed, relayed, dispatched, or forwarded. The conceptmay or may not include the act of listening or waiting for something toarrive from a transmitting entity. For example, a transmission may bereceived without knowledge as to who or what transmitted it. Likewisethe transmission may be sent with or without knowledge of who or what isreceiving it. To “receive” may include, but is not limited to, the actof capturing or obtaining electromagnetic energy at any suitablefrequency in the electromagnetic spectrum. Receiving may occur bysensing electromagnetic radiation. Sensing electromagnetic radiation mayinvolve detecting energy waves moving through or from a medium such as awire or optical fiber. Receiving includes receiving digital signalswhich may define various types of analog or binary data such as signals,datagrams, packets and the like.

“Receiving Station” generally refers to a receiving device, or to alocation facility having multiple devices configured to receiveelectromagnetic energy. A receiving station may be configured to receivefrom a particular transmitting entity, or from any transmitting entityregardless of whether the transmitting entity is identifiable in advanceof receiving the transmission.

“Remote” generally refers to any physical, logical, or other separationbetween two things. The separation may be relatively large, such asthousands or millions of miles or kilometers, or small such asnanometers or millionths of an inch. Two things “remote” from oneanother may also be logically or physically coupled or connectedtogether.

“Satellite Communication” or “Satellite Propagation” generally refers totransmitting one or more electromagnetic signals to a satellite which inturn reflects and/or retransmits the signal to another satellite orstation.

“Signal-to-noise ratio” or “SNR” or “S/N” generally refers to a measurethat compares a level of a desired signal to a level of backgroundnoise. SNR is calculated as the ratio of signal power to noise power,often expressed in decibels. A SNR higher than 1:1 (greater than 0 dB)indicates more signal than noise.

“Size” generally refers to the extent of something; a thing's overalldimensions or magnitude; how big something is. For physical objects,size may be used to describe relative terms such as large or larger,high or higher, low or lower, small or smaller, and the like. Size ofphysical objects may also be given in fixed units such as a specificwidth, length, height, distance, volume, and the like expressed in anysuitable units. For data transfer, size may be used to indicate arelative or fixed quantity of data being manipulated, addressed,transmitted, received, or processed as a logical or physical unit. Sizemay be used in conjunction with the amount of data in a data collection,data set, data file, or other such logical unit. For example, a datacollection or data file may be characterized as having a “size” of 35Mbytes, or a communication link may be characterized as having a databandwidth with a “size” of 1000 bits per second.

“Skip distance” generally refers to the minimum distance from atransmitter to where a wave from skywave propagation can be returned tothe Earth. To put it another way, the skip distance is the minimumdistance that occurs at the critical angle for skywave propagation.

“Skip Zone” or “Quiet Zone” generally refers to an area between thelocation where a ground wave from ground wave propagation is completelydissipated and the location where the first skywave returns usingskywave propagation. In the skip zone, no signal for a giventransmission can be received.

“Skywave Propagation” refers generally to a transmission method in whichone or more electromagnetic-waves radiated from an antenna are refractedfrom the ionosphere back to the ground. Skywave propagation furtherincludes tropospheric scatter transmissions. In one form, a skippingmethod can be used in which the waves refracted from the ionosphere arereflected by the ground back up to the ionosphere. This skipping canoccur more than once.

“Software-Defined Radio” or “SDR” generally refers to a radiocommunication system where components that have been traditionallyimplemented in hardware are instead implemented via software on acomputer and/or embedded system. Some examples of hardware nowimplemented as SDR are mixers, filters, amplifiers,modulators/demodulators, detectors, and equalizers, just to name a few.

“Space-wave Propagation” or sometimes referred to as “Direct WavePropagation” or “Line-of-sight Propagation” generally refers to atransmission method in which one or more electromagnetic waves aretransmitted between antennas that are generally visible to one another.The transmission can occur via direct and/or ground reflected spacewaves. Generally speaking, the antenna height and curvature of the earthare limiting factors for the transmission distances for space-wavepropagation. The actual radio horizon for a direct line of sight islarger than the visible or geometric line of sight due to diffractioneffects; that is, the radio horizon is about ⅘ greater than thegeometric line of sight.

“Spread Spectrum” generally refers to a transmission method thatincludes sending a portion of a transmitted signal over multiplefrequencies. The transmission over multiple frequencies may occursimultaneously by sending a portion of the signal on variousfrequencies. In this example, a receiver must listen to all frequenciessimultaneously in order to reassemble the transmitted signal. Thetransmission may also be spread over multiple frequencies by “hopping”signals. A signal hopping scenario includes transmitting the signal forsome period of time over a first frequency, switching to transmit thesignal over a second frequency for a second period of time, beforeswitching to a third frequency for a third period of time, and so forth.The receiver and transmitter must be synchronized in order to switchfrequencies together. This process of “hopping” frequencies may beimplemented in a frequency-hopping pattern that may change over time(e.g. every hour, every 24 hours, and the like).

“Stratosphere” generally refers to a layer of the earth's atmosphereextending from the troposphere to about 25 to 35 miles above the earthsurface.

“Symbol” generally refers to a waveform, a state or a significantcondition of the communication channel that persists, for a fixed periodof time. For digital baseband transmissions, a symbol may be in the formof a pulse, and a symbol may be in the form of a tone in passbandtransmissions using modems. A transmitter or other device places symbolson one or more channels, and the receiver detects the sequence ofsymbols in order to reconstruct the transmitted data. In some cases,there may be a direct correspondence between a symbol and a small unitof data. For instance, each symbol can encode one or several bits. Thedata may also be represented by the transitions between symbols, and/orby a sequence of several symbols.

“Transceiver” generally refers to a device that includes both atransmitter and a receiver that share common circuitry and/or a singlehousing. Transceivers are typically, but not always, designed totransmit and receive electronic signals, such as analog and/or digitalradio signals.

“Transfer Rate” generally refers to the rate at which something is movedfrom one physical or logical location to another. In the case of acommunication link or communication network, a transfer rate may becharacterized as the rate of data transfer over the link or network.Such a transfer rate may be expressed in “bits per second” and may belimited by the maximum data bandwidth for a given network orcommunication link used to carry out a transfer of data.

“Transmission Line” generally refers to a specialized physical structureor series of structures designed to carry electromagnetic energy fromone location to another, usually without radiating the electromagneticenergy through free space. A transmission line operates to retain andtransfer electromagnetic energy from one location to another whileminimizing latency and power losses incurred as the electromagneticenergy passes through the structures in the transmission line. Examplesof transmission lines that may be used in communicating radio wavesinclude twin lead, coaxial cable, microstrip, strip line, twisted-pair,star quad, lecher lines, various types of waveguide, or a simple singlewire line. Other types of transmission lines such as optical fibers maybe used for carrying higher frequency electromagnetic radiation such asvisible or invisible light.

“Transmission Path” or “Propagation Path” generally refers to a pathtaken by electromagnetic energy passing through space or through amedium. This can include transmissions through a transmission line. Inthis case, the transmission path is defined by, follows, is containedwithin, passes through, or generally includes the transmission line. Atransmission or propagation path need not be defined by a transmissionline. A propagation or transmission path can be defined byelectromagnetic energy moving through free space or through theatmosphere such as in skywave, ground wave, line-of-sight, or otherforms of propagation. In that case, the transmission path can becharacterized as any path along which the electromagnetic energy passesas it is moves from the transmitter to the receiver, including any skip,bounce, scatter, or other variations in the direction of the transmittedenergy.

“Transmission Station” generally refers to a transmitting device, or toa location or facility having multiple devices configured to transmitelectromagnetic energy. A transmission station may be configured totransmit to a particular receiving entity, to any entity configured toreceive transmission, or any combination thereof.

“Transmission Time” generally refers to is the amount of time from thebeginning until the end of a message transmission in a communicationnetwork. In the case of a digital message, the transmission time is thetime from the first bit until the last bit of a message has left thetransmitting node. For a digital packet, the packet transmission timecan be obtained from the packet size and bit rate. The transmission timeshould not be confused with propagation delay which refers to the timeit takes for the first bit to travel from a sender to a receiver.

“Transmit” generally refers to causing something to be transferred,communicated, conveyed, relayed, dispatched, or forwarded. The conceptmay or may not include the act of conveying something from atransmitting entity to a receiving entity. For example, a transmissionmay be received without knowledge as to who or what transmitted it.Likewise the transmission may be sent with or without knowledge of whoor what is receiving it. To “transmit” may include, but is not limitedto, the act of sending or broadcasting electromagnetic energy at anysuitable frequency in the electromagnetic spectrum. Transmissions mayinclude digital signals which may define various types of binary datasuch as datagrams, packets and the like. A transmission may also includeanalog signals.

“Triggering Data” generally refers to data that includes triggeringinformation identifying one or more commands to execute. The triggeringdata and the command data may occur together in a single transmission ormay be transmitted separately along a single or multiple communicationlinks.

“Troposphere” generally refers to the lowest portion of the earth'satmosphere. The troposphere extends about 11 miles above the surface ofthe earth in the mid-latitudes, up to 12 miles in the tropics, and about4.3 miles in winter at the poles.

“Tropospheric Scatter Transmission” generally refers to a form ofskywave propagation in which one or more electromagnetic waves, such asradio waves, are aimed at the troposphere. While not certain as to itscause, a small amount of energy of the waves is scattered forwards to areceiving antenna. Due to severe fading problems, diversity receptiontechniques (e.g., space, frequency, and/or angle diversity) aretypically used.

“Wave Guide” generally refers to a transmission line configured toguides waves such as electromagnetic waves occurring at any frequencyalong the electromagnetic spectrum. Examples include any arrangement ofconductive or insulative material configured to transfer lower frequencyelectromagnetic radiation ranging along the electromagnetic spectrumfrom extremely low frequency to extremely high frequency waves. Othersspecific examples include optical fibers guiding high-frequency light orhollow conductive metal pipe used to carry high-frequency radio waves,particularly microwaves.

It should be noted that the singular forms “a,” “an,” “the,” and thelike as used in the description and/or the claims include the pluralforms unless expressly discussed otherwise. For example, if thespecification and/or claims refer to “a device” or “the device”, itincludes one or more of such devices.

It should be noted that directional terms, such as “up,” “down,” “top,”“bottom,” “lateral,” “longitudinal,” “radial,” “circumferential,”“horizontal,” “vertical,” etc., are used herein solely for theconvenience of the reader in order to aid in the reader's understandingof the illustrated embodiments, and it is not the intent that the use ofthese directional terms in any manner limit the described, illustrated,and/or claimed features to a specific direction and/or orientation.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges, equivalents, and modifications that come within the spirit ofthe inventions defined by the following claims are desired to beprotected. All publications, patents, and patent applications cited inthis specification are herein incorporated by reference as if eachindividual publication, patent, or patent application were specificallyand individually indicated to be incorporated by reference and set forthin its entirety herein.

Reference Numbers 100 communication system 105 information source 110information destination 115 communication channels 120 primarycommunication channel 125 backend communication channel 130 distance 135primary channel latency 140 primary channel bandwidth 145 backendchannel latency 150 backend channel bandwidth 200 communication system204 low latency, low bandwidth communication link 208 high latency, highbandwidth communication link 212 first communication node 216 secondcommunication node 220 atmosphere 224 electromagnetic waves 228transmitting antenna 232 receiving antenna 236 transmission line 240transmission line 244 transmission line 252 repeaters 256 earth 260client 264 connection 266 wireless connection 268 instruction processor272 connection 405 modulator 410 radio transmitter 415 fiber optictransmitter 420 fiber optic cable 425 demodulator 430 radio receiver 435fiber optic receiver 500 communication system 505 transmitter datanetwork 510 receiver data network 600 flowchart 605 stage 610 stage 615stage 620 stage 700 flowchart 705 stage 710 stage 715 stage 720 stage725 stage 730 stage 735 stage 800 message group table structure 900message group table structure 1000 message group table structure 1100flowchart 1105 stage 1110 stage 1115 stage 1120 stage 1125 stage 1130stage 1200 diagram 1205 stage 1210 stage 1215 stage 1220 stage 1225stage 1230 stage 1235 stage 1240 stage 1245 stage 1250 stage 1300decoder system 1305 unframed demodulator data output 1310 decoders 1315priority decoder 1320 shortest length decoder 1325 intermediate lengthdecoder 1330 longest length decoder 1400 diagram 1405 stage 1410 stage1415 stage 1420 stage 1425 stage 1430 stage

1. A method, comprising: creating a message code table that includesmessage groups with different message lengths; assigning higherpreference messages to shorter message length groups and lowerpreference messages to longer message length groups; and communicatingmessages having variable lengths over a communication channel.
 2. Themethod of claim 1, further comprising: wherein preference is based atleast on probability that the message will be sent; wherein thepreference is based at least on financial benefit of the message;communicating the message code table to a receiver for the messages; andtransmitting the message code table over a high latency, high bandwidthchannel. 3-5. (canceled)
 6. The method of claim 2, further comprising:wherein the message code table is created in at least part by a computerat a transmitter; and transmitting the messages using a low latency, lowbandwidth channel.
 7. The method of claim 2, wherein the message codetable is created in at least part by a computer at a receiver, thecommunication channel includes a primary channel, and the primarycommunication channel includes a high frequency radio channel. 8-10.(canceled)
 11. The method of claim 1, further comprising: selecting afinancial trading strategy; developing a set of possible tradingcommands based on the financial trading strategy; estimatingprobabilities that the possible trading commands will be issued;assigning highest probability trading commands to a shortest messagegroup; and assigning next priority commands to a next longer messagegroup that has message lengths longer than the shortest message group.12. A method, comprising: encoding higher preference messages to shortermessage length groups and lower preference messages to longer messagelength groups; communicating the messages having variable lengths basedon said encoding over a communication channel; and wherein saidcommunicating the messages includes transmitting the messages using alow latency, low bandwidth channel.
 13. The method of claim 12, whereinthe preference is based at least on probability that the message will besent.
 14. The method of claim 12, wherein the preference is based atleast on financial benefit of the message.
 15. The method of claim 12,further comprising: communicating the messages using skywavepropagation.
 16. The method of claim 12, wherein the communicationchannel includes a primary channel, and the primary communicationchannel includes a high frequency radio channel.
 17. (canceled)
 18. Themethod of claim 12, wherein the communication channel includes a backendchannel.
 19. The method of claim 12, further comprising: encoding themessages with the variable lengths with at least an error correctioncode; wherein the messages with the variable lengths include at leastforward error correction (FEC); wherein the messages with the variablelengths include at least a checksum; wherein the messages with thevariable lengths include at least a cyclic redundancy check (CRC):appending a newly received symbol for one oft e messages to previouslyreceived symbols; decoding the messages using forward error correction(FEC) and cyclic error correction (CRC); and wherein the messagesconcern one or more high-speed financial trading transactions. 20-25.(canceled)
 26. The method of claim 12, further comprising: increasingerror correction overhead for the messages; providing higher degree oferror protection by increasing error correction overhead; and reducingfalse positives by limiting forward error correction (FEC) to declaringinstead of correcting more symbols than a maximum limit. 27-28.(canceled)
 29. A method, comprising: communicating messages havingvariable lengths over a communication channel; and decoding the messageswithout knowledge of length and timing of the message.
 30. The method ofclaim 29, further comprising: decoding one of the messages using forwarderror correction (FEC); and determining one of the messages is validbased on a validity of a checksum for the message.
 31. (canceled) 32.The method of claim 29, further comprising: decoding the messages usingforward error correction (FEC) and cyclic error correction (CRC). 33.The method of claim 32, further comprising: decoding the messages in aserial manner by cycling through larger message groups.
 34. The methodof claim 32, further comprising: decoding the messages in a parallelmanner by analyzing all potential message group lengths simultaneously.35. The method of claim 29, further comprising: decoding the messages inwhich higher use probability messages are encoded to have a shorterlength as compared to lower use probability messages; and wherein themessages concern one or more high-speed financial trading transactions.36. (canceled)